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EXPERIMENTAL 



PLANT PHYSIOLOGY 



■^- ..BY 

D!^"T:'MACDOUGAL 

University of Minnesota 




NEW YORK 

HENRY HOLT AND COMPANY 
1898 






Copyright, 1895, 

BV 

Henry Holt & COc 

^f^r^^.^:*^^'^^'^- ^^ 






^^ 



ROBERT DRUMMOND. ELECTROTYPER AND PRINTER, NEW YORK 



PREFACE. 



The appreciation shown toward the translation of Oels' 
Pflanzenphysiologische Versuche prepared by the present writer, 
together with the comments and suggestions from laboratories 
in which it has been used, has led to the preparation of this 
manual, which it is hoped will conform somewhat more nearly 
to the needs of American students. The general form of 
Oels' manual has been retained, and many cuts from the 
translation and a few paragraphs of the text have been re- 
peated here without indication of their origin. 

Only the more important and better established portions of 
the subject are treated, and these in the manner already in gen- 
eral use. With the rapid advance of investigation it is next to 
impossible that an elementary laboratory manual should include 
the latest results, especially when the essential points of many 
of them may yet be in controversy and need the critical treat- 
ment which is certainly not within the province of a work of 
this character. In the hands of an instructor in touch with 
current botanical thought, such deficiencies are easily supplied. 

In the interests of precision, the term *' assimilation " is 
here used exclusively to denote a general function of proto- 
plasm, while the term ''photosynthesis," which was introduced 
into the translation of Oels' manual (Preface and page 30), is 
adopted to signify the special process of forming carbohydrates 
from carbon dioxide and water in the presence of chloroph\'Il 
and sunlight. 

The author is indebted to Mr. R. N. Day and Miss J. E. 
Tilden for the demonstration and drawing for Figure 32. 

D. T. MacD. 

Minneapolis, Minn., April 15, 1895. 



CONTENTS. 



PAGE 

Preface iii 

Introduction i 

I. ABSORPTION OF LIQUID NUTRIMENT. 

Food of plants . . . . ^ 3 

Nutrient elements ........... 3 

Distilled water as a nutritive fluid ........ 6 

Influence of iron ............ 6 

Organs of absorption 7 

Zone of root-hairs .9 

Condition of nutrient substances in the soil . . . . . .11 

Nutrition of parasitic plants ......... 10 

Nutrition of saprophytic plants ......... 11 

Physical aspects of plants .......... 12 

Diffusion ............ 12 

Diffusion through epidermis ......... 14 

Power of selection of food-material . . . . . . . .14 

Turgor ^ 16 

II. MOVEMENTS OF WATER IN THE PLANT. 

Root pressure ............ 19 

Transpiration ............ 20 

Evaporation of water fiom leaves ........ 22 

Wilting of excised shoots .......... 23 

Conditions of transpiration ......... 24 

Cause of wilting ............ 26 

Guttation . . .......... 27 

Attraction of soil for water . .27 

Uses of transpiration 28 

Ascent of sap .28 

Path of sap ............. 33 

III. ABSORPTION OF GASES. 

Gases used by the plant • • • • • 35 

Diffusion of gases ........... 36 

Absorption of gases . 36 

V 



vi CONTENTS. 

PAGE 

Photosynthesis 37 

Physical properties of chlorophyll . . . . . . . -39 

Division of the spectrum 40 

Product of photosynthesis 41 

IV. RESPIRATION AND OTHER FORMS OF METABOLISM. 

Nature of metabolism 43 

Respiration 43 

Absorption of oxygen and excretion of carbon dioxide . . . .44 

Liberation of heat 45 

Respiration essential to growth 46 

Fermentation 47 

Changes in color 49 

V. IRRITABILITY. 

Nature of irritability 50 

Perceptive zone, motor zone ....#•... 50 

Geotropism • • • . .51 

Perceptive and motor zones of roots 52 

Amount of influence of gravity 54 

Replacement of gravity 55 

Heliotropism, thermotropism, etc. .••..... 57 

Periodic movements ........... 61 

Hydrotropism ............ 62 

Contact movements ........... 62 

Circumnutation ...... ..e ... 66 

Hygroscopic movements ....•..•.. 66 

VI. GROWTH. 

Nature of growth ........... 68 

Grand period of growth .......... 70 

Influence of light on growth .....••.. 72 

Influence of light on anatomy of leaves . , . , , , .73 
Influence of light and gravity on the formation of organs . . .74 
Influence of temperature on growth . . . . . , . .75 

Sources of heat ............ 76 

Relation of temperature to distribution 76 

Freezing of plants ...... o .... 77 

Relation of moisture to freezing .78 

Lpss of heat 80 

Resting period 80 

Correlation processes ........... 81 

Mechanical force exerted by growing organs .81 

Appendix 84 

Index 87 



EXPERIMENTAL PLANT PHYSIOLOGY. 



INTRODUCTION. 

A PLANT is a living organism which carries on, more or 
less constantly, certain life-processes. The more important 
of these are absorption of food-material, photosynthesis, respira- 
tion, transpiration, secretion, and reproduction. The manner 
in which these processes are performed is largely determined 
by the influence of the external conditions of gravity, light, 
heat, moisture, air, climate, etc. 

In order to obtain an insight into plant life it is necessary 
to consider the nature, purpose, and mutual interaction of the 
life-processes involved and to analyze the influence exerted 
upon them by environment. 

The course of experiments detailed in this manual deals 
only with the more salient features of plant physiology, and 
is illustrative rather than quantitative. In some instances, 
however, the simple treatment given may with proper applica- 
tion yield exact results. The physical and chemical apparatus 
possessed by every college or high school will be found suf- 
ficient to carry out the work. 

Good plant-material is absolutely essential to the profit- 
able performance of the experiments ; and unless a greenhouse 
is at hand, the course should be pursued at a time when plants 
may be grown in the open air. 



METHODS OF EXPERIMENTATION. 

The following books will be found useful for reference : 

Darwin, F. Practical Physiology of Plants. 1894. 

GOODALE. Physiological Botany. 1884. 

Kerner and Oliver. Natural History of Plants. 1894. 

Sachs. Physiology of Plants. 1886. 

Spalding. Introduction to Botany. 1894. 

Vines. Physiology of Plants. 1886. 

Vines. Text-book of Botany. 1894-5. 



METHODS OF EXPERIMENTATION. 

The entire course of an experiment should be described in 
detail in the student's note-book, with reference to the follow- 
ing points : 

1. Object of experiment. 

2. Apparatus and plant-material employed : condition and 
development of the latter. Full drawings. 

3. Date of experiment and successive observations — day 
and hour. 

4. Temperature, moisture, and sunshine. 

5. Results of experiment. 



CHAPTER I. 

ABSORPTION OF LIQUID NUTRIMENT. 

1. Food of Plants. — Green plants generally derive their food 
from simple chemical compounds in the soil, air, and water. 
Of these compounds the simple mineral salts are obtained 
from the soil. Animal manures and decaying vegetable mat-^ 
ter do not serve directly as food-material. Elements and 
simple compounds liberated by the decomposition of these 
substances may be used in building up the plant. The chief 
value of such ** organic" matter to the plant lies in the fact 
that it preserves the porous condition of the soil, thus allow- 
ing access of air to the roots and retaining water containing 
nutrient salts in solution. The decaying '* organic " material 
in the soil also furnishes the proper conditions of growth for 
the soil Bacteria, whose activity is a necessary factor in the 
development of many of the higher plants. An admixture 
of '' organic " material with the mineral elements of the soil 
is also a means of equalizing the temperature. 

Aquatic plants in general use the same food-material as 

land plants. The water in which they grow is in contact 

with the soil and contains all of its soluble salts in solution. 

Remark. — It is to be noted that the species comprised in the parasitic, 
saprophytic, and insectivorous plants, many of which are furnished with 
chlorophyll, are able to use directly complex substances derived from plants 
or animals, and do not depend entirely, or at all, on the simple compounds 
in the soil. 

2. Nutrient Elements. — In order to determine what elements 
enter into the food of plants, and the office of each substance, 

3 



EXPERIMENTAL PLANT PHYSIOLOGY. 



plants may be grown in solutions of different composition. It 
has been found by numerous experiments and analyses that 
only potassium, calcium, magnesium, sulphur, phosphorus, iron, 
and sometimes silica and chlorine are obtained from the soil 
alone. Of the remaining substances necessary for the plant, 
hydrogen is obtained from both water and the soil compounds, 
oxygen from both the soil and the air, nitrogen usually from 
the soil, but in some instances also from the air, and carbon 
almost entirely from the air, except in the case of the plants 
which derive it from complex compounds. (§§ i, 8, and 9.) 

EXPERIMENT i. 

WATER CULTURES. 

Fill a large bottle with distilled water, and to each liter of water 

or 



^dd 

I. gram potassium nitrate 
0.5 " sodium chloride 
0.5 " calcium sulphate 
0.5 " magnesium sulphate 
0.5 " calcium phosphate 
Warm gently for an hour and keep in a dark place. 

Fig. I. 



I. gram calcium nitrate 
0.25 " potassium chloride 
0.25 " magnesium sulphate 
0.25 " acid potassium phos- 
phate 




-Hansen's germinator. Ay glass vessel filled with water and covered with 
tightly-stretched bobbinet. B, bell-jar fitted with moist filter-paper. 
(Oels.) 



ABSORPTION OF LIQUID NUTRIMENT, J 

Place seeds of Wheat, Corn, Bean, Pea, or Buckwheat in folds of 
moist cloth, in a pan of moist sawdust, or in a Hansen germinator 
(Fig. i), until the radicles are a centimeter in length. 

Fill a glass jar or cylinder of a capacity of i to 2 liters with the 
solution described above. The bottle should be well shaken before 
this is done. Add a few drops of iron chloride to the solution in 
the jar. Cut a hole i cm. in diameter through the center of a large 
cork and fit in the top of the cylinder or jar as shown in Fig. 2. 

Fig. 2. 




Culture cylinder with seedling of Corn in position. K, cork. (Hansen.) 



Make a vertical cut from the outer edge of the cork to the. central 
opening. Fasten a seedling obtained as above in the aperture by 
means of cotton-wool or asbestos fiber, in such position that the 
root only is immersed. Set in a sunny place. Renew the solution 
once every week. 

Allow the plant to grow 3 or 4 weeks and compare with others, 
of the same age grown in the soil. 



6 EXPERIMENTAL PLANT PHYSIOLOGY, 

Kemark 1. — To exclude light from the roots and prevent the growth of 
Alga in the culture cylinder it should, be fitted with a jacket of pasteboard 
or blackened paper. This may be still more effectively accomplished if the 
jar is sunk its entire depth in the soil of a large flower-pot or box. If the 
soil is watered occasionally, a temperature more nearly suitable for the 
roots will be obtained. 

Kemark 2. — Calcium phosphate is only slightly soluble in water, and in 
consequence it forms a sediment on the bottom of the jar which decreases 
as that in solution is used. 

Kemark 3. — The sodium chloride used in the first solution is not of 
direct use to the plant, but serves to keep the solution alkaline. 

Kemark 4. — Analysis and agricultural practice show that plants of differ- 
ent species and genera grown in the same soil contain the elements in dif- 
ferent proportions ; consequently a solution suitable for all plants cannot 
be made. Instead of the salts given above, others which contain the ele- 
ments 'in soluble form may be used. The degree of concentration must be 
kept within the prescribed limit, however. 

3. Distilled Water as a Nutritive Fluid. — A plant will grow 
for a time in distilled water, but when the food stored in the 
seed is consumed it perishes. 

EXPERIMENT 2. 

DISTILLED WATER AS A NUTRITIVE FLUID. 

Grow two seedlings as nearly alike as possible, one in distilled 
water and the other in a nutritive solution as in Experiment i. 
Note difference in lo and 14 days. 

4. The Influence of Iron. — The plant can form green color- 
ing matter {chlorophyll) only when supplied with iron. If 
this is withheld, the plant dies after it has used the iron stored 
in the seed. The presence of chlorophyll is necessary for the 
formation of food from the carbon dioxide of the air. (§ 29.) 

EXPERIMENT 3. 

IRON-FREE NUTRITIVE SOLUTION. 

Grow two plants in an iron-free nutritive solution. The first 
leaves are green and the later ones pale yellow (chlorotic)^ 

EXPERIMENT 4. 

ADDITION OF IRON TO A CHLOROTIC PLANT. 

Pour a few drops of iron solution into the culture jar of a chlo- 
rotic plant obtained by Experiment 3. The leaves soon become 
green. With a small brush moisten portions of a leaf of another 



ABSORPTION OF LIQUID NUTRIMENT, 7 

chlorotic plant with iron solution. The portions treated will become 
green in a short time, and this color will gradually extend over the 
plant. 

5. Organs of Absorption. — In the lower plants or simple or- 
ganization the absorption of nutriment is carried on by a greater 
part or all of the surface of the organism. In the higher 
plants the roots are the special organs of absorption, and 
nearly all of the liquid taken in by the plant is obtained 
through them. The marked branching shown in the root sys- 

Fig. 3. 




Cross-section of a root showing structure and arrangement of root-hairs. 
The latter are swollen in places, applying a broader surface to the soil- 
particles in contact with them. (Frank.) 

tem of the higher plants not only increases the efficiency of 
the roots as organs for the fixing of the plant in the soil, but 
also magnifies the absorbing surface. Absorption is carried 
on through the outer walls of the peripheral cells which con- 
stitute the epidermis. In land plants the outer walls of these 
epidermal cells are developed into long tubelike extensions, 



8 



EXPERIMENTAL PLANT PHYSIOLOGY. 




the root-hairs (Fig. 3). The amount of surface extension ob- 
tained by root-hairs is very great, since these structures are 
.008 mm. to .14 mm. in diameter, and often attain a length of 
3 mm., while from 10 to 400 may be formed on a square 
millimeter of surface. 

The root-hairs are also an adaptation for obtaining water 
Fig. 4. under the conditions in which it is 

found in the soil, where it occurs in the 
form of a minute layer on the surface 
of the soil-particles. The root-hairs 
are capable of bending around and 
penetrating between the particles in a 
manner which places their walls in con- 
tact with a large amount of this layer 
of water. In aquatic plants root-hairs 
are not needed, and are rarely formed, 
since the entire body of the root is in 
contact with the water. It will be seen 
that the land plants grown in water in 
the cult^are experiments developed very 
few root-hairs. On the other hand, 
plants grown in dry soil exhibit a very 
marked development of these struc- 
tures. In this instance the amount of 
Seedlings of White Mus- water around each soil-particle is very 

tard. (Sachs.) A, with 

soil clinging to the roots ; small, and the plant must reach a 

B, after removal of the , , , r ,-, . -, 

mass of soil by washing, much larger number of them m order 
to obtain the needed supply. 

EXPERIMENT 5. 

ADHESION OF ROOT-HAIRS TO SOIL-PARTICLES. 

Grow seedUngs of Mustard, Pea, or Corn in sandy soil. When 
one week old take up and note amount of soil clinging to roots 
(Fig. 4). Free from the mass of the soil by washing. Examine 



ABSORPTION OF LIQUID NUTRIMENT. 



with a magnification of lo to 25 diameters and observe the remain- 
ing soil-particles attached to the irregular root-hairs. 



EXPERIMENT 6. 



STRUCTURE OF ROOT-HAIRS. 



Cut a thin cross-section of the root of a seedling grown in the 
germinator and examine with a magnification of 50 to 100 diameters. 
Note the tubelike structure of the hairs, the thin irregular layer of 
protoplasm on the inner side of the wall and the large transparent 
central portion filled with sap. Examine the base of the hair and 
note its relation to the neighboring cells of the root (Fig. 3). 

6. Zone of Root-hairs. — As the root extends in length by 
the growth of a portion near the tip, new root-hairs constantly 
arise in this region, while the older ones in the region farther 
away are constantly dying. The zone of root-hairs ordinarily 
begins i to 3 cm. back of the tip and extends backward along 
the root for a distance of about 5 to Fig. 5. 

10 cm. In this manner new root-hairs 
are continually brought into contact 
with fresh particles of soil. 

EXPERIMENT 7. 

f 

MOVEMENT OF ZONE OF ROOT-HAIRS. 

. Place a germinated . seed of Pea or 

Squash in a small funnel or thistle-tube 

in such manner that the root extends 

downward in the narrow outlet. Cover 

the seed with moist cotton and place a 

layer of moist filter-paper and a glass 

plate over the top of the funnel to prevent . . 

. ^ Apparatus to demonstrate 

the seedling from becoming dried. Set progression of zone of 

the funnel upright in a bottle containing root-hairs. (After Oels.) 

. ° A, potassium hydrate 

a small amount of a solution of potassium solution ; Z, moist filter- 
hydrate. This solution will absorb the P^per. 
carbon dioxide gas given off by the seedling. By means of India 
ink mark on the glass tube the boundaries of the zone of root- 
hairs every day during a week. (Fig. 5.) 




lO 



EXPERIMENTAL PLANT PHYSIOLOGY. 



7. Condition of Nutrient Substances. — Only liquid nutriment 
is taken up by the roots. The mineral substances of the soil 
are slowly dissolved by percolating water which contains small 
amounts of oxygen and carbon dioxide, as well as traces of 
nitric and sulphuric acids derived from the air. In some cases 
the walls of the root-hairs are saturated with an acid sap, 
which aids in the solution of the mineral salts. 

EXPERIMENT 8. 

ACIDITY OF ROOTS. 

Place the roots of a seedling of Pea, Bean, or Corn grown in a 

germinator, on a sheet of blue litmus 
paper. The portion of the paper 
touched becomes red, indicating the 
presence of an acid. 

EXPERIMENT 9. 

CORROSIVE ACTION OF ROOTS. 

Fill a 5-inch pot half full of 

moist loam. On this lay a piece of 

marble whose upper surface is highly 

polished. Fill the pot with moist 

sand and imbed a germinated pea 

or bean near the surface. After the 

soil has been thoroughly penetrated 
Marble plate«,rroded by roots. ^^ ^^^ ^^^^^ (^^ ^^ ^^ ^^^^^ ^^^^ 

out the marble plate, dry, and by re- 
flected light note the rough lines etched on its upper surface by the 
acid of the roots. 

8. Nutrition of Parasitic Plants. — Many plants of which 
Mistletoe and Cuscuta are examples do not develop a root 
system for the absorption of nutriment from the soil, but 
attach themselves to the bodies of other plants, from which 
they derive sap containing the necessary substances already 
prepared. Such plants are termed parasites. In many cases 
parasitic plants are entirely devoid of chlorophyll and depend 
altogether on the host-plant for their food. Cuscuta (Dodder), 




ABSORPTION OF LIQUID NUTRIMENT. II 

Epiphegus (Beechdrops), and the microscopic Rusts and Smuts 
are examples of plants of this latter type. Mistletoe and many 
other parasitic plants are furnished with chlorophyll and are 
able to obtain a portion of their food-supply from the simple 
compounds. 

EXPERIMENT lo. 

NUTRITION OF CUSCUTA. 

Examine plants of any ordinary species of Impatiens growing 
in wet or swampy ground, in September. On some of these plants 
may be found the yellowish cordlike twining stems of Cuscuta, 
bearing knotty masses of pale yellow or cream-colored flowers. 
With the plants still in position note that the Cuscuta has no soil- 
roots, but that it sends short haustoria or suckers into the stem of 
the Impatiens. With a sharp knife cut across the stem of the host- 
plant and determine the depth to which the haustoria have pene- 
trated. The haustoria obtain sap from the host-plant by osmose, in 
a manner similar to the action of the root-hairs of land plants. 

9. Nutrition of Saprophytic Plants. — Many plants derive 

all or a large proportion of their food-material from the 

products of the metabolism (see Chapter IV) of other organ 

isms. Such plants are termed saprophytes. Examples of this 

type are afforded by Corallorhiza (Coral-root), Monotropa 

(Indian-pipe), Toadstools, Mushrooms, and many Bacteria. 

EXPERIMENT ii. 

NUTRITION OF TOADSTOOLS. 

Note the growth of Toadstools and other Fungi on pieces 
of decaying wood in a damp forest. Tear apart the mass on which 
the plants are growing, and trace the long irregular absorbent organs 
ramifying in all directions through the mass. 

EXPERIMENT 12. 

NUTRITION OF MOULDS. 

Place a fragment of saturated bread under a moist bell-jar for 
two days. A number of slender hyphce of a Mould may be seen 
springing from the bread. Tear apart a small bit of the bread 
and examine with a magnification of 50 diameters. The absorbent 
mycelia can be seen branching in all directions. 



12 EXPERIMENTAL PLANT PHYSIOLOGY, 

EXPERIMENT 13. 

NUTRITION OF BACTERIA AND RELATED FORMS. 

Make a solution of sugar in a cylinder and set in a warm room 
for three days. A film or scum will be formed on the surface of 
the liquid. Under a magnification of 600 diameters the scum will 
be found to consist of an immense number of globular, cylindrical, 
or spiral cells of Bacteria and other forms which obtain their food 
from sugar and complex substances formed by other plants. 
These organisms absorb food-material through their entire surface. 
The spores of such plants are found floating in the air and develop 
whenever they come in contact with food under proper conditions.^ 
of temperature. 

10. Physical Aspects of a Plant. — From a purely physical 
point of view the plant may be regarded as a cylindrical 
chamber whose walls are composed of membrane, and whose 
contents consists of a large number of stable and unstable 
compounds dissolved in water. At both ends of the cylinder 
the surface is magnified, at the lower end in the roots and 
root-hairs, and at the upper end in the leaves, to facilitate the 
diffusion of gases and liquids. The body of the cylinder, the 
stem, acts as a tubelike conductor between these surfaces. 
The outer layer of the stem is not easily permeable by fluids. 

11. Diffusion. — By diffusion is understood any exchange 
which may take place between two fluids in contact either 
directly or through a membrane. This latter exchange is 
termed osmose. Diffusion takes place regardless of gravity 
until the fluids are alike. Not all fluids are capable of osmose, 
but only those which are imbibed by a membrane. The 
rapidity of diffusion varies with the mobility of the fluids. 
Stable compounds diffuse with more difficulty than waten 
Concentrated solutions of these compounds increase in volume, 
since they gain more water than they lose. They occur in the 
root-hairs, and in consequence a large quantity of water is 
taken up and forced into the root and upward in the stem. 



ABSORPTION OF LIQUID NUTRIMENT, 



13 



EXPERIMENT 14. 

OSMOTIC ACTION OF A SUGAR SOLUTION. 

Cover the large end of a thistle-tube or small glass funnel with 
rightly-stretched membrane, such as parchment or bladder, which 
has been soaked for 15 minutes in water. Fill the large part of the 
tube or funnel with a solution of sugar i part and water 3 parts, and 
fasten upright by means of a large perforated stopper in a cylinder 
containing water, in such position that the two fluids are on a level. 
Note the height of the solution in the tube in 12 and 24 hours. A 
large amount of water has been drawn through the membrane into 
the sugar solution, while only a small portion of the latter has passed 

out into the cylinder, as can be ascertained by 

tasting. (Fig. 7.) 

EXPERIMENT 15. 

OSMOTIC ACTION OF A SOLUTION OF COPPER SULPHATE. 

Cover one end of 
an ordinary lamp-chim- 
ney tightly with hog's 
bladder or parchment, 
fill with a solution of 
copper sulphate, and 
suspend in a vessel of 

Fig. 9. 



Fig. 7. 



Fig. 8. 





Osmometer. (Miil- 
ler.) b, bulb of 
thistle -tube ; D, 
level of liquid in 
cylinder; r^Ievelof 
liquid in tube after 
a few hours' opera- 
tion. 




Carrot hollowed 
out and filled 
with sugar. 
(Miiller.) 



d 

o 

coating formed on an 

copper-sulphate soluti 

distilled water. (Fig. 



Osmometer. (Oels.) 
K, cork to hold 
lamp-chimney in 
place ; c, open end 
of lamp-chimney. 

istilled water. After a time the bluish color 

f the water in the vessel, and the copper-red 

iron nail placed in the vessel, denote that the 

on has passed through the membrane into the 

) 



14 EXPERIMENTAL PLANT PHYSIOLOGY. 

EXPERIMENT i6. 

OSMOSE IN PLANT-TISSUES. 

Hollow out the central part of a large Carrot, making the walls 
of the cavity formed about .5 cm. in thickness. Fill the cavity with 
dry sugar. Twenty-four hours later the sugar will be dissolved in 
the sap which is drawn into the cavity, while the Carrot is dry and 
shrunken. 

12. Diffusion through Epidermis of Aerial Organs. — Roots and 
root-hairs are pre-eminently organs of absorption, yet in some 
instances leaves and stems exercise this function. The leaf- 
like organs of Mosses and Liverworts are capable of absorbing 
water. 

EXPERIMENT 17. 

WATERPROOFING OF LEAVES. 

Cut off a leaf of the Cabbage, Oak, Beech, or Iris and immerse 
in water. The surface takes on a silvery appearance, due to the 
thin layer of air adhering to it. An examination will show a 
heavy layer of cuticle or waxy substance on the outer side of the 
epidermis. 

EXPERIMENT 18. 

ABSORPTION OF WATER BY LEAVES. 

Cut off a young branch of Coleus, Geranium, Tomato, Impatiens 
or other convei.ient plant and seal the end with wax or gum. Lay 
aside until slightly wilted. Immerse entirely in a vessel of water. 
Examine in two hours. If the leaves are capable of absorbing 
water, they will be restored to their original condition. It will be 
found that few plants can take water by means of the leaves. A 
moist atmosphere prevents loss of water, but does not form a source 
of supply for the plant. 

13. Power of Selection of Food-material. — The root-hairs are 
immersed in a solution of mineral salts in the soil in a manner 
similar to the thistle-tube in Experiment 14. By the laws of 
diffusion all of these substances should be absorbed by the 
root-hairs until an osmotic equilibrium is established, and gen- 



ABSORPTION OF LIQUID NUTRIMENT, 



15 



erally such is the case. The amount of any one substance 
necessary to estabhsh equiHbrium is very small, and as soon as 
this amount is acquired, absorption of that substance ceases. 
When the plant withdraws any of the substances from the cell- 
sap solution to build up tissue, another quantity of that sub- 
stance is absorbed from the soil. Thus different quantities of 
the various substances are absorbed. It is to be noted that 
all substances in the soil are not invariably extracted even in 
the minutest quantity by any one plant. The '' rotation of 
crops" has its value for the farmer because different plants do 
not require the same soil-salts. 

EXPERIMENT 19. 

INCREASED DIFFUSION. 

Close the lower end of two lamp-chimneys with bladder or 

Fig. 10. 





Apparatus to show selective diffusion. (After Oels.) K K, corks, loosely 
fitted ; C C, copper-sulphate solution. 

parchment and fill with distilled water. In the upper end of one 
cylinder place a stopper into which several iron nails have been 
driven. Make a saturated solution of copper sulphate and place 
exactly the same amounts in both cylinders. Now fasten the two 
chimneys in the cylinder as shown in Fig. 10. In 48 hours take out 



i6 



EXPERIMENTAL PLANT PHYSIOLOGY. 



the chimneys and note that a bright deposit of copper has formed 
on the nails. Pour some granulated zinc into each cylinder. lu 
24 hours take out the undissolved zinc, and filter the solution in 
both jars, to obtain the copper precipitate. Allow the precipi- 
tate to remain on the filter-paper and dry. Weigh. It will be 
found that a much smaller quantity is obtained from the solu- 
tion in the apparatus containing the nails. The action of the 
iron nails in withdrawing the copper from the solution inside the 
lamp-chimney, thus causing an additional amount to be taken up 
from the outside^ will show the manner in which a plant exercises 
a " selective power " of absorption. 

When a living cell, composed of protoplasm 
enclosing the cell-sap and surrounded by 
the wall, is placed in contact with water it 
absorbs the water in such quantity that the 
wall is stretched, while on the other hand 
the wall tends to contract by its own elas- 
ticity. Thus a cell-tension is set up which 
is denoted turgor (Fig. 11). The cells 
composing many of the tissues do not 
absorb water, while others take up large 
quantities and expand in consequence. 
If now a tissue which absorbs much water 
is attached to another which remains pas- 
sive, a strain, or tissue-tension, will be set 
up. These tissue-tensions give rigidity 
to herbaceous plants. The wilting of plants is accompanied 
by loss of turgor, and consequent decrease of the tissue- 
tensions. 




Diagram of cell. (Har- 
tig.) a, c, wall ; b 
protoplasm ; d, nucle 
us ; e, cell-sap. 



EXPERIMENT 20. 

TURGOR IN AN ARTIFICIAL CELL. 

Cover one end of an open glass cylinder 10 cm. in length (a 
large tube will suffice) with membrane, fill with a sugar solution, 
close the other end in the same manner, and place in a vessel 



ABSORPTION OF LIQUID NUTRIMENT. 



17 



containing water. The contents of the cylinder increase in volume 
by absorption of water, and the membranes take a convex form 
in consequence of the increased pressure inside the cylinder. 
Place the cylinder in a vertical position and pierce the upper mem- 
brane with a needle. The liquid spurts upward from the pressure. 

(Fig. 12.) 

Fig. 12. 




Artificial cell to illustrate force of turgor. (After Oels.) 
EXPERIMENT 21. 

IMBIBITION (osmose) OF WATER BY SEEDS. 

Ascertain the exact weight of 20 dried Peas, and place in a 
dish containing distilled water. In 24 hours the Peas will have 
greatly increased in size by the diffusion of water through the 
seed-coat. The substances stored in the seed have a strong attrac- 
tion for water. Dry the seeds by rubbing with a cloth, and weigh. 
In some cases they will have taken up their own weight of water. 
The force of the osmose may be shown if a bottle of 25 cc. capacity 
is filled with the seeds and immersed in a vessel of water for 24 
hours. 

EXPERIMENT 22. 



LONGITUDINAL TISSUE-TENSIONS. 

Cut a slice a centimeter in thickness and 

Fig. 13. 



10 cm. in 



length 







Longitudinal tissue-tensions. (Hansen.) a, outward curvature of a sec- 
tion due to excess of turgor of pith ; b, length of separated tissues ; 
m m, pith (parenchyma). 



EXPERIMENTAL PLANT PHYSIOLOGY. 



Fig. 14. 



from the centre of a young branch of Elder (Sambucus) or stem 
of Rhubarb. Divide the slice in halves and note the outward 
curvature of the two parts. Describe the 
tensions which existed. Prepare another 
slice and separate the parenchyma (pith) 
from the wood and epidermis. The pa- 
renchyma expands and the other portions 
contract. (Fig. 13.) 

EXPERIMENT 23. 

TRANSVERSE TISSUE-TENSIONS. 

Cut a ring of bark from a young twig of Transverse tissue-ten- 
Willow or Poplar, and after a few minutes sions. (Detmer.) 

replace in its original position. It now does not extend entirely 
around the twig. When in that position it must have been in a 
stretched condition. (Fig. 14.) 




CHAPTER II. 

MOVEMENTS OF WATER IN THE PLANT. 

15. Root-pressure. — The roots, by reason of the osmotic 
activity of the substances which they contain, are constantly 
absorbing water. The amount taken up during the winter 
season when the soil is either frozen or at a very low tempera- 
ture is very small. At the* beginning of spring the storage 
products which were accumulated in the roots during the latter 
part of the previous season are changed into substances, such as 
sugar, dextrine, asparagin, etc., which are soluble and possess, 
great osmotic activity. At this season the leaves are not yet 
formed, and only a limited amount of water is carried up and 
transpired by the plant ; consequently the water taken in by 
the roots is slowly forced upward in a stream, almost filling 
the wood-cells in the lower part of the plant. The action of 
the roots is well illustrated by the osmometer described in 
Experiment 14. The pressure with which the water is forced 
upward by a Nettle will sustain a column of water 3 or 4 meters 
high. In the Grape the root-pressure is sufficient to sustain a 
column of water 10 meters in height. A yearly periodicity 
of root-pressure is noticed in trees and other perennial plants. 
In addition it can be demonstrated that daily variations due 
to temperature of soil and air and the humidity of the air occur. 
In the Grape the pressure is greatest in the forenoon, and 
decreases from 12 to 6 P.M. The root-pressure of the Sunflower 
reaches its maximum and begins to decrease at 10 A.M. 

19 



20 



EXPERIMENTAL PLANT PHYSIOLOGY, 



EXPERIMENT 24. 

MEASUREMENT OF ROOT-PRESSURE. 

Cut off the stem of an actively-growing plant of Dahlia, Geranium, 
Corn, Sunflower, or Grape a short distance above the ground, and 



Fig. 15. 



fasten tightly to the stump in a perpen- 
dicular position a long glass tube by 
means of a short section of rubber tubing. 
Observe the varying height of the sap 
in the tube from day to day, noting the 
temperature and moisture of the air at the 
same time. (Fig. 15.) 

16. Transpiration. — The water taken 
up by the roots finds its way upward 
through the stem toward the leaves, 
where a constant diffusion into the air 
takes place. The diffusion of water 
from the leaf or other organs of a 
plant into the air is designated trans- 
piration. Transpiration takes place 
under the same physical laws as the 
evaporation of water from a moist 
membrane. Barometric pressure, light, 
temperature, humidity, and move- 
ments of the air are the most impor- 
tant conditions affecting the process. Apparatus for demonstra- 
tion of root-pressure. 
The amount of water actually given off (Detmer.) 

varies also with certain metabolic processes (see Chapter IV.). 
A plant may be compared to a tube filled with water, with 
an expanded upper end closed by a membrane, while the 
lower end is immersed in water. By evaporation an upward- 
flowing stream is set in motion. 

EXPERIMENT 25. 

LIFTING-POWER OF THE EVAPORATION OF WATER FROM A MEMBRANE. 

Fill a thistle-tube by placing it in a vessel of water, and while in 
that position cover the large end by a tightly-stretched membrane. 




MOVEMENTS OE WATER IN THE PLAINT. 



21 



Close the small end of the tube with the finger, lift from the water, 
and place in an upright position with the small end immersed in a 
dish of mercury. (Fig. i6.) Examine daily for two weeks or more. 
As the water evaporates the mercury slowly rises. It may be drawn 
to a height of 34 cm. if a good quality of ox-bladder is used. 

Fig. 17. 



Fig. 16. 





Apparatus to demonstrate lifting power of evaporation. (After Oels.) 

This experiment may also be carried on in the following manner 
to determine the amount of water evaporated : Fit a thistle-tube 
with a membrane as above, and while still under water attach to it 
by means of a short section of rubber tubing a glass tube bent twice 
at right angles (Fig. 17). Completely fill the apparatus with water 
and fasten in an upright position. Place a drop of oil on the surface 
of the water in the open tube to prevent evaporation at this point. 
The amount of evaporation from the membrane will be shown 
directly by the fall of the level in the open tube. 



22 



EXPERIMENTAL PLANT PHYSIOLOGY, 



17. Water Evaporates from Leaves as from a Membrane. — The 

shoots and leaves of plants give off water in a manner similai 
to the action of the apparatus in the above experiments. 

EXPERIMENT 26. 

LIFTING-POWER OF TRANSPIRATION. 

By means of a closely-fitting rubber stopper fasten a leafy shoot 
of a woody plant (Raspberry, Rosebush, etc.) in one end of a U tube 
filled with water and Fig. 19. 

mercury. The mercury 
in the open arm of the 
tube soon begins to sink, 
indicating a loss of water 
from the leaves. (Fig. 
t8.) This fact may alsc 
be demonstrated by fit- 
ting the shoot to the 
upper end of a straight 
tube whose lower end is 

Fig. 18. 





Lifting power of transpira- 
tion. (After Oels.) a, 
water; b, mercury. 



Lifting power of transpiration. 
(Detmer.) 



MOVEMENTS OF WATER IX THE FLA XT. 



23 



immersed in mercury. (Fig. 19.) The lifting power of transpira- 
tion can be estimated from the height of the mercury column. 

EXPERIMENT 27. 

ESTIMATION OF THE TRANSPIRATION FROM A SINGLE LEAF. 

Fasten a leaf with around smooth petiole in one end of a U tube 
by means of a rubber stopper. Previously fill the U tube with 
water and fit in the other end a long capillary tube bent at right 
angles. Place the apparatus in such position that the leaf will be 



Fig. 20. 
b 




Apparatus for estimation of trans- 
piration. (Mangin.) The water 
recedes from a toward b. 



held upright, and the long arm of the small tube horizontal (Fig. 
20). A small amount of transpiration from the leaf will cause the 
water in the small tube to recede horizontally. The amount and 
rate of transpiration may be easily computed. 

18. Wilting of Excised Shoots in Water. — Herbaceous 

shoots when cut off and set in water generally wilt quickly, 

but if the shoot is cut under water it remains fresh a much 

longer time. Evidently the cause of the wilting when the 

stems are cut without this precaution is the penetration of the 

shoot by air. Perhaps in rapidly-growing plants escaping slime 

may seal up the ends of the vessels which conduct water. 

EXPERIMENT 28. 

WILTING OF SHOOTS EXCISED IN AND OUT OF WATER. 

Bend a long shoot of a slightly woody plant (Symphytuip, Rose- 
bush, etc.), so that a portion of the stem is under the surface of the 



24 



EXPERIMENTAL PLANT PHYSIOLOGY. 



water in a dish. Cut off the stem under water, and it will remain- 
fresh several days if the cut end is kept immersed. At the same 
time cut off another shoot in the air, and after lo minutes place the 

Fig. 21. 




Excision of a shoot under water. (After Oels.) 

cut end in the vessel of water with the other shoot. Compare 
results daily. (Fig. 21.) 

19. Conditions of Transpiration. — Plants transpire water con- 
stantly over their entire aerial surface, yet the stems and the 

Fig. 22. 

c 




Stoma from under side of leaf of Iris florentina. c, cuticle. (Strasburger.) 
greater part of the leaves are covered with an almost impervious 
layer of cuticle. Beside this, the devices exhibited by plants, 
especially those growing in the dri&r regions, by which trans- 



MOVEMENTS OF WATER IN THE PLANT. 2$ 

piration may be lessened or controlled, are very numerous. One 
of the most effective is a covering of branching hairs. Much the 
greater part of the water thrown off by the plant is transpired 
from the thin-walled cells in the interior of the leaf into the inter- 

FiG. 23. 



Air-chamber and opening of Marchantia polymorpha : magnified 300 times. 

(Kerner.) 

cellular spaces which communicate with the open air through 
the stomata. The stornata (Figs. 22 and 23) are openings in 
the epidermis, which are controlled by guard-cells. When 
more water is transpired from the leaf than is furnished by the 
roots, the guard-cells become flaccid, and the walls are thick- 
ened in such manner that in this condition these cells change 
their form and close the openings of the stomata entirely. 
When the necessary water-supply is at hand the guard-cells are 
turgid and the stoma remains open. The action of the guard- 
cells is also influenced by light, wind, and other factors. 
Transpiration is increased by heat, light, dryness, high pres- 
sure, and movements of the air, and lessened by the opposite 
conditions. 

EXPERIMENT 29. 

INFLUENCE OF HUMIDITY ON THE AMOUNT OF TRANSPIRATION. 

Place a well-leaved Begonia grown in a pot, on one pan of a drug- 
gist's balance. Cover the soil by means of two glass plates, or tie a 
piece of oiled cloth around the entire pot, to prevent evaporation. 



26 EXPERIMENTAL PLANT PHYSIOLOGY, 

By means of weights on the other pan equalize the balance. In an 
hour it will be noted that the end of the scale holding the plant has 
risen. Take weights from the other pan until the equipoise is restored. 
The amount of the weights taken off will represent water transpired 
by the plant. After balancing cover the plant by means of a bell- 

FiG. 24. 



Estimation of amount of transpiration by weighing. (After Oels.) 

jar. In an hour remove the bell-jar, quickly wipe from the pan the 
water which may have condensed and run down the sides of the 
bell-jar, and again take off weights to balance. The amount lost 
will be less than before. The air in the bell-jar soon becomes satu- 
rated with water and checks transpiration. (Fig. 24.) 

EXPERIMENT 30. 

INFLUENCE OF EPIDERMIS ON TRANSPIRATION. 

Select two Apples and two Potatoes of equal size. Peel one of 
of each. Weigh and set aside for three hours. Again weigh. It 
will be seen that a waxy or corky epidermis retards transpiration 
very efficiently. 

20. Wilting. — If the amount of water transpired exceeds 
that absorbed by the roots, wilting results. This may occur 
from the destruction of the root-hairs or from an insufficient 
supply of water in the soil. In the transplantation of trees the 
branches are trimmed in order that the transpiring surface 
may be reduced in proportion to the absorbing surface. The 
latter — in the root-hairs — is nearly all destroyed by transplan- 



MOVEMENTS OF WATER IN THE PLANT, 2/ 

tation. The turgor of a wilted plant may be restored either 
by watering the soil or checking transpiration. 

EXPERIMENT 31. 

RESTORATION OF A WILTED PLANT BY CHECKING TRANSPIRATION. 

A plant if not too badly wilted will revive if placed under a bell- 
jar or if transpiration is checked by other means. 

21. Guttation. — If the amount of water absorbed by the 
roots is in excess of that transpired by the leaves, it will exude 
through rifts in the epidermis, or the water-pores^ in the form of 
drops. This process is termed guttation. It may be observed 
in plants at the end of a warm day. The air cools quickly, 
and its relative humidity is increased while the roots absorb 
the same amount of water from the soil, which retains its 
warmth for a longer time. 

EXPERIMENT 32. 

GUTTATION PRODUCED BY CHECKED TRANSPIRATION. 

Cover a plant such as Corn, Wheat, or Pea with a bell-jar and 
place in sunlight. Note the drops of water on the leaves after an 
hour or two. 

22. Attraction of Soil for Water. — Plants cannot either by 

the force of diffusion or of transpiration absorb all of the 

water in the soil. Absorption finally reaches a limit beyond 

which the attraction of the soil-particles for water is stronger 

than the combined force of diffusion and evaporation in the 

plant. 

EXPERIMENT 33. 

AMOUNT OF WATER IN THE SOIL WHICH CANNOT BE ABSORBED. 

Grow a plant (Bean) in a pot filled with rich garden soil. As 
soon as the primordial leaves have developed, place in a room ex- 
posed to direct sunlight, and allow it to remain without watering until 
it wilts. Now take a sample of a few grams of the soil which has 
been penetrated by the roots, and dry at 100° C. for an hour. Weigh. 
It is demonstrated that the soil contained a large percentage of 
water which the plant could not obtain to replace its evaporation. 



28 EXPERIMENTAL PLANT PHYSIOLOGY, 

23. Uses of Transpiration. — In the economy of the plant 
transpiration is of the greatest importance. Water and dis- 
solved nutrient salts are carried to the leaves by the transpira- 
tion stream. The greater part of the water evaporates, and 
the remainder, with the salts, is formed into compounds useful 
to the plant. In the leaves the simple ^^ power of selection'' 
operates as in the roots, and only the salts they can use are 
carried to them in quantity. It is probable that transpiration 
serves other uses which are not yet clearly understood. The 
suggestion has been made that it equaHzes changes of tempera- 
ture in the plant. 

24. Ascent of Sap. — The forces concerned in carrying water 
from the roots to the leaves are root-pressure, capillary action 
of the wood-cells, imbibition, diffusion, expansion and contrac- 
tion of the air-bubbles in the wood-cells, transpiration, and 
osmotic action of the protoplasm of the wood-parenchyma 
cells. 

In small herbaceous plants root-pressure is almost always 
present, and it acts with a force sufficient (see paragraph 15) to 
drive water to the leaves. In plants of this character the suc- 
tion exerted by transpiration is also sufficient to carry water 
upward to the desired height. (See Experiment 26.) The 
other factors mentioned are of minor importance in such 
plants. 

In trees, however, which may attain a height of 10 to 150 
meters, the manner in which the necessary water-supply is 
carried to the leaves becomes a question of great complexity. 
Root-pressure is present in trees only during a limited period 
at the beginning of the growing season and is almost entirely 
absent in summer when the greatest amount of water is used. 
Hence it cannot bear a very important part in the ascent of 
sap. The transpiration of water from the leaves creates a 
vacuum in the stem below, as has been demonstrated in 



MOVEMENTS OF WATER IN THE PLANT. 29 

Experiment 26. (See also Experiment 35.) The suction thus 
caused would not raise water higher than a suction-pump 
(about 10 meters). The water, however, is not in a continuous 
tube like the cylinder of a pump. The rectangular wood-cells 
are in the form of a series of chains. The water in each cell 
is separated from that of the neighboring cells by a thin mem- 
brane which promotes osmose. Water is transpired from the 
topmost cells of these chains, the cell-sap becomes concen- 
trated and draws water from the cells beneath, and they in turn 
from those beneath them. There is thus formed a series of 
osmometers extending from the leaves to the roots, and 
capable of lifting water to any height. 

In gassing from the lower to the upper end of the narrow 
wood-cells, the ascent of sap is greatly retarded by capillary 
friction. On the other hand, the cavity of a w^ood-cell con- 
tains a bubble of gas, which by its expansion and contraction 
aids in forcing the sap upward. Further, imbibition by the 
cell-wall allow^s the passage from one part of the plant to 
another of a small amount of water which does not enter the 
cell-cavities. 

It is difficult to account for the rapidity of sap-movements 
by the action of these physical iorces alone. Some investiga- 
tions tend to show that the protoplasm of the wood-parenchyma 
has a rhythmic osmotic attraction for water. Some such force 
is necessary to account for all features of sap-movement in 
trees. 

EXPERIMENT 34. 

AMOUNT OF WATER FORCED UPWARD BY ROOT-PRESSURE COMPARED WITH 
THAT TRANSPIRED BY THE LEAVES OF AN HERBACEOUS PLANT. 

With a sharp knife cut off a strongly growing Sunflower plant 
near the ground. Fasten the upper part with its cut end in a 
measuring-cylinder containing water. To the stump (lower part) 



30 



EXPERIMENTAL PLANT PHYSIOLOGY. 



fasten by means of rubber tubing a tube bent twice at right angles. 
Insert the free end of the tube in a test-tube. The water thrown 
out and through this tube by root-pressure will be collected in the 
test-tube, and its volume can be compared with the amount drawn 
out of the measuring-cylinder by the transpiration of the other part 
of the plant (Fig. 25). 

Fig. 25. 




Comparison of root-pressure and transpiration. (After Oels.) 



MOVEMEXTS OF WATER IX THE FLAXT. 



31 



EXPERIMENT 35. 



Fig. 26. 




NEGATIVE PRESSURE. 

In September bore a small hole 6 cm. 
in depth in the trunk of a small Birch, 
and fit into the opening a glass tube a 
meter in length which has been bent 
once at right angles. Make the fitting 
'• air-tight " by means of wax. Place 
the lower end of the tube in a dish of 
mercury. In a day or two the mercury 
will rise in the tube to a varying height. 
The rapid transpiration from the leaves 
has withdrawn so much water from the 
trunk of the tree that a partial vacuum 
is formed. (Fig. 26.) This may also 
be demonstrated as follows (Fig 27) • 



Negative pressure in Birch 
stem. (After Oels.j 






^-Jfk 




1 




\h 


' 

^ 


""!• 


^^- 






;;r. 



Negative pressure in shoot of Lonicera. (Detmer.) 



32 



EXPERIMENTAL PLANT PHYSIOLOGY, 



Cut off a shoot of some woody plant with tender leaves (Loni- 
cera), and place the lower end in a vessel of water. Now cut off 
the top and fasten to the end of the shoot, by means of a piece of 
rubber tubing, a glass tube bent twice at right angles. Place the end 
of the perpendicular long arm in a vessel of mercury. In a short 
time the fluid ascends in the tube. 

EXPERIMENT 36. 

RESTORATION OF SAP-CURRENT. 

Fix an excised shoot of Coleus or Helianthus (Sunflower) by 
means of a rubber stopper in one arm of a U tube and fill with water. 

Its power of conduction has been de- 
stroyed and it wilts (See Experiment 28). 
Now pour mercury into the free arm of 
the tube. The turgor is restored, and is 
retained until the mercury is higher 
under the plant than in the other arm. 

EXPERIMENT 37. 

RATE OF ASCENT OF SAP. 

Water copiously the soil in which a 
herbaceous plant i meter in height is 
growing, with a solution of lithium ni- 
trate. In an hour cut a portion from 
the tip and at successive intervals 
toward the root. Burn these pieces 
in the flame of an alcohol-lamp or Bun- 
sen burner, and by the characteristic 
red flame of lithium ascertain to what 

Restoration of sap-current, height the lithium has ascended in the 
(Sachs.) g^^^^ 

EXPERIMENT 38. 

MOVEMENT OF FLUIDS IN CONTINUOUS VESSELS. 

Cut away the stem of a Euphorbia (Spurge), Sonchus (Wild 
Lettuce), or Asclepias (Milkweed). The milky juice exudes rapidly 
from both the upper and lower cut surfaces in a manner indicative 
of pressure. Cut away the stem of a Gourd or Pumpkin and note 
the large drops of slime which must have been forced from some 
distance, since that amount would not be found in the cells of the 
part cut across. 




MOVEMENTS OF WATER IN THE PLANT. 



33 



25. Path of Sap Movements. — The plant takes up water and 
mineral salts from the soil, and forms foods from carbon diox- 
ide in the leaves. These substances must pass from the roots 
upward and from the leaf downward to be of use to the plant. 
The ascending stream moves upward through the woody part 
{xylem) of the stem. In trees the greater amount passes 
Fig. 29. Fig. 30. 




Cross-section of portion of shoot of Cross-section of portion of stem 
Sambucus nigra (Elder) magnified 15 of Sambucus nigra (Elder) 
times. (After Oels.) e, epidermis ; magnified 150 times. (After 
^, cork ; r/, parenchyma and scleren- Oels.) rp, phloem paren- 
chyma ; c, cambium ; h, wood ; w/, chyma ; sc, sclerenchyma ; c, 
pith. cambium ; h, wood ; ;;/, me- 
dullary rays. 

through five or six of the recently-formed annual rings, as may 
be seen in trees with hollowed trunks which sustain tops of nor- 
mal size. The descending current passes through the soft inner 
bark, the phloem. The descending current moves very slowly, 
and is carried on principally by diffusion (Figs. 29 and 30). 

EXPERIMENT 39. 

UPWARD PATH OF SAP. 

Remove a ring of the bark and soft wood from any young 
tree or woody shoot a few centimeters above the ground by means 
of a sharp knife. The shoot shows no disturbance for a time vary- 
ing from a few weeks to many months, when the roots become starved 
from lack of food usually supplied by the leaves and perish. 



34 



EXPERIMENTAL PLANT PHYSIOLOGY, 



EXPERIMENT 40. 

DOWNWARD PATH OF SAP. 

In the same manner as above girdle a Willow branch i to 3 
cm. in diameter by removing a ring of bark near the lower end. 
Fig. 3i» 




Place upright with the lower end sub- 
merged in water. The buds develop in a 
normal manner while roots are formed on the 
lower end, but only above the girdling ring. 
Since the phloem is removed, the food-mate- 
rial necessary for the formation of the roots 
cannot pass the ring. (Fig. 31.) 

EXPERIMENT 41. 

DEMONSTRATION OF PATH OF SAP BY COLORED 
FLUID. 



Girdled shoot of Sambu- 
cus. (After Oels.) 



Cut off a semi-transparent stem of Impa- 
tiens (Touch-me-not), and place the lower end 
in a water solution of some aniline color. In an hour note that the 
colored fluid has ascended in the woody fibres in the soft stem. 
Repeat, using a stalk of a young Corn plant. Allow it to stand in 
the solution 24 hours, then dissect and determine the path of the 
fluid. 



CHAPTER III. 

ABSOPTIOX OF GASES. 

26. Grases used by the Plant. — Of the gaseous elements 
which enter into the food of plants, hydrogen is taken up in 
the form of water or ammonia by ordinary green plants, while 
it forms a large proportion of the complex substances which 
are used by parasitic and saprophytic plants. Oxygen is ob- 
tained from the air in a free state, and in combination in the 
form of water, carbon dioxide, and the mineral salts. Nitrogen 
is derived chiefly from compounds in the soil. Leguminous 
plants and many groups of the lower forms are able to take 
up this element directly from the atmosphere. The greater 
part of it used by the higher plants has been fixed in the soil 
by the action of Bacteria and related forms. At the present 
tim^e the power of the various groups of plants to take up free 
nitrogen is not clearly defined. Carbon is obtained by plants 
which do not contain chlorophyll from the complex compounds 
which they use as food. This is true of all plants which use 
complex foods. Green plants, however, obtain their carbon 
supply from the carbon dioxide of the air. (§ 29.) 

27. Diffusion of Gases. — If two gases that will mix are sepa- 
rated by a membrane, they will pass through the membrane b\' 
osmose in the same manner as liquids. The air is a mixture 
of 77.95 parts of nitrogen, 20.61 parts of oxygen, 1.40 parts 

35 



3^ EXPERIMENTAL PLANT PHYSIOLOGY. 

of aqueous vapor, and .04 part of carbon dioxide. These 
gases are in different proportions in the plant and conse- 
quently a constant diffusion through the outer membrane 
takes place. Some cells containing substances which have a 
high osmotic equivalent for oxygen absorb it from the air. 
In like manner cells containing chlorophyll take up carbon 
dioxide during the daytime. Gases will readily diffuse 
through a membrane, yet cannot be forced through it by 
pressure. 

EXPERIMENT 42. 

DIFFUSION OF GAS THROUGH EPIDERMIS. 

Smooth one end of a glass tube with an internal diameter of .5 
cm. and a length of 30 cm. in a flame. Select a smooth and perfect 
grape. Take off the skin and clean the pulp from the inside. 
Place over the end of the tube, bringing the edges down and fasten- 
ing closely to the tube by a small cord. (Fig. 32.) With Paling- 
wax secure the edges to the glass in such a manner as to be *^ air- 
tight." Test by placing in water and forcing air in at the other end. 
If no bubbles escape, fill the tube with water and invert in a vessel 
of mercury. Displace the water with carbon dioxide and note the 
height of the mercury column daily for a month. By the diffusion 
of the carbon dioxide through the membrane the column of mercury 
may be raised as high as 26 cm. 

Remark. — In inverting the tube when fuU of water no air must be 
aUowed to gain entrance. To obtain carbon dioxide use the apparatus de- 
scribed in Experiment 57. Marble and hydrochloric acid should be used 
instead of zinc and sulphuric acid, as there described. 

28. Absorption of Hydrogen, Oxygen, and Nitrogen. — The 

absorption of hydrogen, oxygen, and nitrogen, and their 
synthesis into food are so closely connected with other 
complex metabolic processes that a consideration of the 
separate action in each case is somewhat difficult. The 
manner in which carbon is obtained and used is, however, 
a fairly distinct process. 



ABSORPTION OF GASES, 



37 



29. Photosynthesis. — Green plants absorb carbon dioxide 



from the air either through 
the epidermis or the stomata. 
Carbon dioxide is composed 
of one part of carbon and two 
parts of oxygen. The proto- 
plasm which forms the mass 
of the green color bodies 
(chlorophyll bodies) in the 
cells has the power, when it 
receives the sunlight, of sep- 
arating one part of the oxy- 
gen which is thrown off as 
a free gas, while the carbon 
monoxide which remains is 
combined with the water 
present to form a compound 
of carbon, hydrogen, and 
oxygen from which sugar is 
ultimately derived. The en- 
tire process may be desig- 
nated photosynthesis. No 
life is imaginable without 
photosynthesis. All organ- 
isms, plants, and animals 
alike are ultimately depend- 
ent upon the products of 
this process for their carbon compounds 



Fig. 32. 




Diffusion of gas through epidermis. 
/, level of mercury column 20 days 
after beginning of experiment ; O, 
skin of grape ; T, sealing-wax ; D , 
centimeter-scale. 



EXPERIMENT 43. 

THE ACTION OF LIGHT IS NECESSARY FOR PHOTOSYNTHESIS. 

Weigh 4 seeds of Corn, germinate and grow in nutrient soUition. 
Place 2 of the seedlings in a dark chamber and the remaining 2 in 
the sunlight. In three weeks take the plants from the solutions, dry 



38 



EXPERIMENTAL PLANT PHYSIOLOGY, 



in the air for several days and weigh. Those in darkness will have 
lost, while those in light will have gained weight since they were able 
to form food from carbon dioxide of the air and water. 

EXPERIMENT 44. 

OXYGEN IS GIVEN OFF DURING PHOTOSYNTHESIS. 

Fill a funnel of medium size with green shoots of Elodea 8 to 10 
centimeters in length. Immerse the funnel, inverted, in a wide dish 
filled with spring-water, and over the small end of the funnel place 
a test-tube filled with water. Set in the sunlight. In a short time 



Fig. 33. 



Fig. 34. 





Apparatus to show excretion ot 
oxygen by Elodea. (Detmer.) 



Action of light on Elodea. 
(After Oels.) 



gas can be seen, collected in the upper part of the tube, which tested 
with a glowing splinter is proved to be oxygen. 



EXPERIMENT 45. 

THE AMOUNT OF PHOTOSYNTHESIS AND OF OXYGEN GIVEN OFF DEPENDS ON 
THE INTENSITY OF THE LIGHT. 

Fasten a shoot of Elodea about 10 centimeters long to a glass 
rod and immerse in spring-water or water containing carbon dioxide, 
so that the cut end is higher than the other. Set the apparatus in 
direct sunlight, and immediately a stream of gas-bubbles — oxygen — 
begins to pour from the cut end of the shoot. (Fig. 34.) In diffused 



ABSORPTION OF GASES. 



39 



light, or in light the intensity of which is reduced by means of one 
or more plates of ground glass (Fig. 35), the number of bubbles 



Fig. 35. 




Box blackened on the inside. (After Oels.) a a, ground-glass plates ; b^ 

shoot of Elodea. 

given off decreases, so that the dependence of photosynthesis upon 
light can be seen directly. 

30. Physical Properties of Chlorophyll. — Chlorophyll is a sub- 
stance of extremely complex and unstable constitution. It is 
generally found in certain definite masses of protoplasm in the 
cell, although in some plants it appears uniformfy diffused 
throughout. Its presence is sometimes masked by other color- 
ing matter, as in the Red Sea-weeds and colored leaves of the 
foliage plants of the garden. Some of the autumnal tints of 
leaves are due to coloring substances resulting from the oxida- 
tion of chlorophyll. The spectrum of sunlight which has 
passed through a solution of chlorophyll in alcohol shows 
several dark bands. The portions of light thus absorbed are 
converted into heat and other forms of energy needed for 
photosynthesis and other processes. If different portions of the 
spectrum are allowed to act on a plant, the relative amount of 



40 



EXPERIMENTAL PLANT-PHYSIOLOGY, 



photosynthesis promoted by each can be demonstrated. The 
red rays are principally active in photosynthesis. 

31. Division of the Spectrum.— It is found that a watery solu- 
tion of potassium bichromate transmits only the red, orange, 
and yellow rays of light, and that an ammoniacal solution of 
copper oxide transmits only the blue and violet rays. Unless 
carefully compounded, however, the latter solution will also 
allow the passage of some of the red and yellow rays. 

EXPERIMENT 46. 

PORTION OF THE SPECTRUM ACTIVE IN PHOTOSYNTHESIS. 

Make a solution of potassium bichromate in water. To obtain 
the ammonia-copper-oxide solution, add ammonium hydrate to a 
solution of copper sulphate in water as long as the forming precipi- 
tate is redissolved. Fill a double-walled bell-jar with each solution. 



Fig. 36. 



Fig. 37. 





mmismsm 



Double-walled bell-jar. 
(After Oels.) 



Apparatus to replace double 
walled bell-jar. (After Oels.) 
k, solution of potassium bi- 
chromate or copper oxide; w, 
water ; />, pasteboard cover. 



Prepare three shoots of Elodea as 

in Experiment 45. Place one in 

sunlight and one under each bell-jar 

off from the shoots in open sunlight and under the red bell-jar, but 

none from the one under the blue bell-jar. (Fig. 36.) 



Bubbles of oxygen are given 



ABSORPTION OF GASES, 



41 




If the double-walled bell-jars are not at hand, each may be re- 
placed by two glass cylinders, one so much larger Fig. 38. 
than the other that when the smaller is fastened in- 
side the other by means of a cork, a space of about 
I to 2 cm. remains between them. Fill this space 
with the proper solution, and the inner vessel with 
water containing carbon dioxide, and place in the 
latter the plant-shoots. To cut off the perpendicu- 
lar rays cover the apparatus with a loosely-fitting 
cardboard cover. (Fig. 37.) The pasteboard box 
shown in Fig. 35 can also be used if instead of the 
ground-glass plates {a a) parallel-walled glass cells 
filled with the absorption fluid are used. With colored Apparatus to 
glass plates only an approximately pure light can be demonstrate 
obtained. If the box is used, it will be found most of oxygen, 
convenient to place the shoot in an inverted test-tube (Mangm.) 
filled with water as in Fig. '^'^. The amount of gas can be measured 
directly in the tube. 

32. Product of Photosynthesis. — The product of photosyn^ 
thesis IS probably some soluble carbohydrate such as glucose.. 
As soon as enough of this substance has been formed to meet, 
the immediate needs of the plant the remainder is converted 
into starch. If the plant is placed in darkness or under any 
condition in which it cannot carry on photosynthesis, as soon 
as the glucose in the cells is consumed the starch is recon-^ 
verted into glucose or some form of sugar and assimilated. 
The amount of starch present in a plant may be taken as 
an indirect indication of the amount of photosynthesis. 



EXPERIMENT 47. 

MACROCHEMICAL TEST FOR STARCH. 

Boil a few leaves of Bean, Tomato, or Tropaeolum for a few 
minutes to kill the protoplasm and swell the starch-grains present. 
Place in warm alcohol until the chlorophyll is dissolved. Bring 
the leaves into an alcoholic solution of iodine for a half-hour. 
The leaves will be colored a dark blue if they contain starch. 



42 EXPERIMENTAL PLANT PHYSIOLOGY, 

EXPERIMENT 48. 

MICROCHEMICAL TEST FOR STARCH. 

Decolorize some filaments of Spirogyra, or leaves of Funaria as 
above, and place on a glass slide in a drop of chloral hydrate 
(chloral hydrate 5 parts, water 2 parts). Add a drop of a solution 
of iodine in iodide of potassium, and examine with the microscope. 
A thin section of large leaves may be examined in this manner. 

EXPERIMENT 49. 

STARCH AS AN INDICATION OF PHOTOSYNTHESIS. 

Place some Spirogyra or Vaucheria in a dark chamber for 24 
hours. Test some of the filaments for starch. It will be found 
absent. Set the vessel containing the filaments in the sunlight for 
a few minutes. Examine a second lot. Starch will be found 
present. 

EXPERIMENT 50. 

FORMATION OF STARCH FROM SUGAR. 

Deprive a Geranium plant of starch by placing in a dark cham- 
ber for 24 hours or longer. Test for starch, and if none is present 
cut off a leaf and place it in a 20^ solution of sugar for a week in a 
dark chamber. Test for starch. The protoplasm of the leaf has 
used the sugar as food and has also converted a portion of it into 
starch. 



CHAPTER IV. 

RESPIRATION AND OTHER FORMS OF METABOLISM. 

33. Nature of Metabolism. — By various processes, of which 
photosynthesis is an important example, a large number of 
complex substances are formed in the plant. The synthesis of 
complex compounds from those of simpler composition is 
termed cojistimctive metabolism. In this process a portion of the 
oxygen in the simple compounds is liberated. Thus in photo- 
synthesis water and carbon dioxide, both containing oxygen, 
are combined and a portion of the oxygen is set free. This 
liberation of oxygen makes constructive metabolism what is 
known in chemistry as a reducing process. On the other hand, 
when the complex foods thus formed are used by the plant, 
oxygen is taken up and the complex substances are resolved 
into others of simpler composition. This is known as destruc- 
tive metabolism. Since oxygen is absorbed in destructive meta- 
bolism, it is essentially an oxidizing process. One of its most 
important forms is respiration. 

34. Respiration. — In respiration, which is directly opposite 
in character to photosynthesis, oxygen is absorbed, carbon 
dioxide given off, and energy liberated in the forms of heat 
and electricity. The oxygen needed is largely obtained from 
the air, although in some instances it is derived from com- 
pounds in the plant which contain a large proportion of it. 
The extraction of oxygen from one substance within the 

4.3 



44 



EXPERIMENTAL PLANT PHYSIOLOGY. 



plant for the oxidation of another is termed intramolecular 
respiration. This form of respiration is carried on to some 
extent by all plants, but is characteristic of the germination of 
oily seeds and of Yeast, Bacteria, etc. 

Respiration is essentially the same process in both plants 
and animals, but while the former breathe and give off carbon 
dioxide constantly from all parts of their bodies, the latter, 
in the highly-developed forms, breathe rhythmically and for 
the greater part by means of organs especially adapted for the 
purpose. Yet there are instances among both plants and 
animals where the respiratory processes are suspended or re- 
duced for a period of varying length. 

35. Absorption of Oxygen and Excretion of Carbon Dioxide.— 
The amount of carbon dioxide given off in respiration is 
Fig. 39. Fig. 40. 




Liberation of carbon dioxide by 
respiration. (Mangin.) a, 
baryta-water. 

approximately equal to the 
oxygen taken up. The 
proportion of the two sub- 
stances varies with the tem- 
perature and other condi- 
tions, and in the different organs. De Saussure found that i 
gram of seed of Hemp absorbed 19.7 cc. of oxygen and exhaled 




Cylinder containing germi- 
nating Peas. (Sachs.) 



RESPIRATIOX AXD OTHER FORMS OF METABOLISM. 45 

13.26 cc. of carbon dioxide in the same time, and i gram of seed 
of Madia absorbed 15.83 cc. of oxygen, while it exhaled 11.94 
cc. of carbon dioxide. Young growing plants will exhale an 
amount of oxygen equal to their own volume in 24 to 36 
hours. 

EXPERIMENT 51. 

EXCRETION OF CARBON DIOXIDE BY LEAVES. 

Provide a ground-glass bell-jar and plate. Under the bell-jar 
place a well-leaved plant grown in a pot, and a vessel containing 
lime- or baryta-water ; place the apparatus in darkness. After a 
short time a film of carbonate can be seen on the surface of the fluid 
which, if allowed to remain longer, collects as chalk (or baryta). As 
a control experiment, set up the same apparatus without the plant. 
The lime- or baryta-water is scarcely affected. (Fig. 39.) 

EXPERIMENT 52. 

EXCRETION OF CARBON DIOXIDE BY GERMINATING SEEDS. 

Fill a glass jar of i liter capacity one-third full of Peas which 
have lain a day in water. Cover tightly. After 12 or 14 hours a 
light thrust in is extinguished, showing the lack of oxygen, and a 
vessel containing lime- or baryta-water placed inside demonstrates 
the presence of carbon dioxide. Instead of Peas, developing heads 
of a Composite or some large Fungus can be used. (Fig. 40.) 

36. Liberation of Heat. — In very strong respiration, as in 
the development of flower-heads of the Compositae, flower-tubes 
of the Aroids, and germinating seeds, enough heat is liberated 
in the combustion of the carbon compounds of the plant to 
be easily detected by the thermometer. Sachs observed in 
100 to 200 germinating Peas a rise in temperature of 1.5° C. 
(Fig. 41.) 

EXPERIMENT 53. 

HEAT LIBERATED BY GERMINATING SEEDS. 

Fill a glass funnel of medium size with germinating Peas 
or blooming heads of Leontodon, Anthemis, Bellis, etc., into which 
a thermometer graduated to \ degree C. has been thrust. To avoid 



46 



EXPERIMENTAL PLANT PHYSIOLOGY, 



loss of heat as far as possible, cover the funnel with a perforated 
glass plate, whereby access of air is prevented. The carbon dioxide 



Fig. 41. 



formed is absorbed by a solution of 
potassium hydrate which is placed in 
a glass dish under the funnel. As a 
comparison place near this apparatus 
a thermometer in the free air which 
will not be affected by the heat of 
the plants. To obtain the most uni- 
form temperature for both thermom- 
eters cover each with a large bell-jar. 

37. Eespiration, Essential to 
Growth and Dependent on Air. — The 
conversion of food into living sub- 
stance is possible by means of 
respiration only. The higher plants 
may carry on a certain amount of 
Apparatus to demonstrate liber- intramolecular respiration and thus 

ation of heat in respiration. ^ 

(Sachs.) accomplish a small amount of 

growth. For the normal development of the plant, however^ 
it is necessary that it have access to the free oxygen of the air., 

EXPERIMENT 54. 

OXYGEN NECESSARY FOR RESPIRATION. 




Fill two respiration-tubes of 100 cc. 
capacity with water which has been 
boiled to drive off the dissolved air. In 
the bulbs of each insert a half-dozen 
seeds of Pea or Wheat, and invert over 
a dish of mercury. Twenty-four hours 
later displace nearly all of the water in 
one tube with hydrogen and the other 
with air. The seeds in hydrogen do not 
germinate, while those in air, which are 
able to obtain their customary supply of 
oxygen, develop normally. To obtain 
the hydrogen, place a few grams of gran- 



FiG. 42. 




Respiration-tubes. (Detmer.) 
A, filled with hydrogen, 
and By oxygen. 



ulated zinc in a flask or bottle, and cover to a depth of 5 cm. 



RESPIRATION AND OTHER TOR MS OF METABOLISM. 47 

with diluted sulphuric acid. Close the mouth of the flask with a 
cork stopper through which extends a short section of glass tubing. 
To the outer end of this attach a section of rubber tubing 30 cm. 
in length. The free end of the rubber tube should be fitted with 
a small piece of glass tubing drawn to a point and bent at an angle 
of 45 degrees for introducing the gas into the respiration-tube. 
(Fig. 42.) 

38. Fermentation. — Perennial plants which grow in temper- 
ate climates store up a supply of reserve food in the roots, 
rhizomes, or stems, to serve as building material at the begin- 
ning of the next vegetative period. The seedling cannot 
obtain nourishment from the soil and air during the first period 
of its development, because its roots are not sufficiently de- 
veloped, and because it has not yet enough chlorophyll to build 
up food, by aid of the sunlight. Before the solid reserve sub- 
stances can become of use to the plant they must be dissolved, 
and transported by diffusion w^here they are needed. The 
solution of the reserve food is accomplished by means of fer- 
ments or enzymes^ which by their presence induce changes in 
organic compounds (^fermentation) without themselves being 
thereby in any way affected. On account of this last property 
a small amount of enzyme may cause fermentation in a large 
quantity of the substance acted upon. In the germination of 
a seed, external moisture and temperature stimulate the proto- 
plasm to form an enzyme which dissolves the solid starch, 
protein, or fat in the storage cells. The solution is diffused 
into the growing cells of the young plant where it is used in 
building up protoplasm. The starch formed in leaves under- 
goes solution and transportation in a similar manner. Diastase, 
the enzyme which changes starch into maltose, is perhaps the 
most widely distributed ferment. 



48 EXPERIMENTAL PLANT PHYSIOLOGY, 

EXPERIMENT 55. 

ACTION OF DIASTASE. 

Place 10 grams of seed of Barley in a germinator for 36 hours, 
or until the radicles are .5 cm. in length. Grind fine, in an ordi- 
nary coffee-mill, and add to three parts of water. After a time filter 
and mix the filtrate, which now contains diastase, with a fifth part 
of very thin starch paste (i gram starch, 100 grams water). A 
sample of this mixture is colored blue on treatment with iodine, a 
sample taken later, violet, then brown, and finally one taken after 
two or three hours is colorless, demonstrating that all the starch 
has been transformed into maltose or sugar by the diastase present 
in the germinated seed. 

Cut thin sections of the seeds at the beginning of the experiment 
and determine the appearance and characteristics of the starch- 
grains. Make a similar examination 24 and 48 hours later. Allow 
germination to proceed in a few seeds, and examine 4 days later. 
The starch-grains are gradually corroded and dissolved by the 
diastase formed. 

EXPERIMENT 56. 

TRANSLOCATION OF STARCH. 

A Tropseolum plant whose leaves are rich in starch is placed in 
the dark after some of its leaves have been cut off. The excised 
leaves are likewise placed in the dark in a moist room or under a 
l)ell-jar. After a few days test some of the excised leaves and those 
remaining on the plant for starch. Those on the plant show some 
starch, mostly in the nerves, while those excised show starch in the 
other parts as well, because they could not transfer it to other 
organs. 

EXPERIMENT 57. 

FORMATION AND TRANSLOCATION OF STARCH. 

On a well-developed plant of Tropaeolum majus standing in the 
sunlight in the forenoon, darken portions on some healthy leaves, by 
means of cork plates, fastened on opposite sides by pins. On the 
afternoon of the following day cut off the leaves and boil in water 
in a porcelain dish for a few minutes, to kill the protoplasm. Ex- 
tract the coloring matter by alcohol many times renewed. The de- 
colorized leaves are now saturated with alcoholic iodine in a porce- 



RESPIRATION AND OTHER FORMS OF METABOIISM. 49 



lain dish, whereupon they will be colored a deep blue except in 
shaded portions. Since, substantially, starch-formation in the leaf 
proceeds by day only, and the solution and translocation at night 
as well, the places exposed to the sunlight contain enough starch to 

Fig. 43. b 





a, Tropaeolum leaf to which are attached two pieces of cork to prevent pho- 
tosynthesis. (Detmer.) b, same after removal of cork, treated with 
iodine. 

give the microscopic reaction with iodine. It was taken away from 
the shaded places at night, however, and could not be replaced. 
(Fig. 43-) 

39. Changes in Color. — Many changes in the chemical com- 
position of substances in the plant are accompanied by corre- 
spending changes in color. (See Chlorophyll, Par. 30.) Flow- 
ers which are blue when fully opened were originally red in the 
bud. The sap was acid at first and became alkaline as the result 
of metabolic changes. Leaf-colors offer similar conditions, 
although the changes in color here are sometimes due to the 
oxidation of chlorophyll and other coloring matter in the cells. 

EXPERIMENT 58. 

RELATION OF RED AND BLUE COLORS OF FLOWERS. 

Immerse a leaf of Begonia bearing red hairs, for a short time in 
a weak solution of ammonia. The hairs become blue. Place a 
blue petal of Myosotis in a \io solution of acetic acid. It becomes 
reddish. Express the sap from a handful of petals of Roses or 
Peonies. Collect in a test-tube and add a few drops of ammonia. 
A blue color results. Add some acid. The red color is restored. 
Observe the different colors assumed by leaves in the autumn. 



CHAPTER V. 

IRRITABILITY. 

40. Nature of Irritability. — The term irritability designates 
that property of plants by which they respond to certain influ- 
ences known as stimuli. The stimuH may be either internal 
forces set in operation by metabohc activity or external influ- 
ences, such as gravity, light, temperature, electricity, moisture, 
and mechanical contact. The plant may react in two ways, 
first, by changes in the structure, form, and size of its organs ; 
second, by motion or change in position of its organs or of the 
protoplasmic bodies in its cells. The reactions of the first class 
concern growth ; those of the second class result in placing 
plant or cell organs in certain positions relative to the direction 
of the stimulus. Thus a plant grown in darkness develops its 
stems and leaves in quite different form and structure from 
one grown in the open air (Fig. 6^), Light, then, affects the 
structure and form of plants by what is known as its formative 
or tonic influence. (See Chapter VI.) Light also causes shoots 
to bend toward its source in such manner as to place their 
axes parallel to the light-rays. This is termed its directive in- 
fluence. A stimulus may give rise to reactions of both kinds 
at the same time, and they cannot always be easily and dis- 
tinctly separated by experiments. 

41. Perceptive and Motor Zones. — The action of an external 
stimulus on one part of a plant does not necessarily cause a 
movement in that part, but the impulse may be transmitted to 
a region more or less distant. Thus, for instance, a touch on the 

leaf-blade of a Mimosa (Sensitive-plant) causes no contraction 

50 



IRRITABILITY. 51 

in the leaf-blade, but the impression is transmitted to the pul- 
vinus at the base of the leaf or leaflet and produces movement. 
The region which receives the stimulus is designated the/^r- 
ceptive zone, and the one which causes the movement, the 
motor zone. The two may coincide in position. 

42. Geotropism. — The power by which a plant responds to 
the influence of gravity is termed geotropism. The response 
of an organ to this stimulus may occur in three ways, as follows. 
(i) The organ may point its apex toward the centre of the earth, 
the source of gravity, in w^hich instance it is said to be pro^ 
geotropic. This action is generally manifested by primary 
roots. (2) It may point its axis away from the source of gravity, 
directly upward, when it is said to be apogeotropic. Erect 
shoots are generally apogeotropic. In general organs of 
radial structure exhibit one of these two forms of geotropism. 
(3) The organ may place its axis in a horizontal position, at 
right angles to the force of gravity, when it is said to be dia-^ 
geotropic. This is characteristic of the larger number of bilateral 
organs, such as leaves, although also shown by organs of radial 
structure, such as branches of stems, secondary roots, etc. 

EXPERIMENT 59. 

PROGEOTROPISM. 

To a cork in the top of a bell-glass fasten a seedling of a 
Bean with the radicle which is i 

to 2 cm. in length in a horizontal ^^^'- -^'+- 

position. In a few hours the tip 
is found to be pointing downward 
more or less directly. (Fig. 44.) 

EXPERIMENT 60. 



GEOTROPIC REACTIONS OF SEEDLINGS. 

Place a layer of sawdust be- 
tween two horizontal parallel rings ^'rogeotropism of seedling. (Det- 
^ ^ mer.) b, dish partly filled with 
covered with wide-meshed gauze. water ; g, bell-glass ; s, seedling. 




52 



EXPERIMENTAL PLANT PHYSIOLOGY, 



Plant seeds of the Pea, Bean, or Corn in the sawdust. The roots 

Fig. 45. pass through the meshes downward and the 

shoots upward. Invert the apparatus and these 

organs will bend in the opposite directions. 

(Fig. 45-) 

Fig. 46. 








"Geotropism of roots and 
shoots. (After Oels.) 



Apogeotropism of leaves of Onion. 
(Frank.) 



EXPERIMENT 61. 

APOGEOTROPISM. 

Place a Tulip, Hyacinth, Onion, or Fritillaria, which is growing 
rapidly, in a horizontal position. In a short time the leaves curve 
•directly upward. (Fig. 46.) 

EXPERIMENT 62. 

DIAGEOTROPISM. 

Observe the opening flower-buds of a Narcissus, which at first are 
erect, but later the perianth-tube assumes a horizontal position. 
After they have attained this position lay the pot on its side with 
the leaves and stems horizontal and the perianth-tube pointing 
downward. In 10 hours the pedicels will have again curved to 
place the perianth-tube in the same position as before. 

43. Perceptive and Motor Zones of Roots. — The stimulus of 
gravity is received by a sensitive portion near the tip of a root 
(the perceptive zone), and an impulse is conveyed to a region 
several millimeters distant which curves (the motor zone). 



IRRITABILITY, 



53 



The motor zone in this instance is located in the region of 
most active growth. (See Experiment 86.) 

EXPERIMENT 63. 

PERCEPTIVE ZONE OF ROOTS. 

Repeat Experiment 59 after cutting away a portion of the tip 
of the root i to 2 mm. in length. The root does not now respond 
to gravity, and shows no movement until the tip is rehabilitated, when 
it curves downward in a natural manner. 

EXPERIMENT 64. 

MOTOR ZONE OF ROOTS. 

With a fine brush carefully mark off equal spaces (2 to 3 mm.) on 



Fig. 47. 




Motor zone in roots. (Pfeffer.) 



the primary root of a seed- 
ling of Phaseolus (Bean). 
Suspend in a horizontal 
position in a moist chamber. 
In a day note the region 
in which curvature has 
occurred, and its distance 
from the tip. 

EXPERIMENT 65. 

MOTOR ZONES OF CULM OF 
GRASS. 

Cut a length of 12 cm. 
from a vigorously growing 
culm of Grass. Place in a 



horizontal position in a moist chamber with one end imbedded 
in sand. Six hours later note the region of curvature. The motor 
zone will be found in the Fig. 48. 

pulvinus like internodes. (Fig. 
48.) 

EXPERIMENT 66. 

FORCE OF CURVATURE. 




Fasten a seedling of Pea 
with a radicle i cm. in length 
to a piece of cork attached to 
the side of a vessel containing' 
mercury. Place the seedling in such position that the root is 



Curvature of Culm of Grass. 
(After Oels.) 



54 



EXPERIMENTAL PLANT PHYSIOLOGY. 




horizontal and the tip is in contact with the mercury. Pour in 
enough water to form a thin layer on top of the mercury. The 
root will bend downward with such Fig. 49. 

force as to penetrate the mercury. 
(I^^ig- 49-) 

44. Influence of Gravity. — 
Gravity acts in a vertical direc- 
tion and with a force directly 
proportioned to the mass of the 
body acted upon. In plants the amount and rapidity of the 
curvature of an organ, in response to gravity, depends on 
its stage of development and the angle which its axis forms 
with the vertical. Progeotropic organs respond most rapidly 

Fig. 50. 



Root of seedling penetrating 
mercury. (Sachs.) 




Seedlings on a revoi'ving wheel driven by a clock. (After Oels.) 



IRRITABILITY. 55 

when their tips are pointing upward at an angle of 45 degrees 
from the vertical ; apogeotropic organs respond most readily 
when pointing downward at an angle of 45 degrees ; and dia- 
geotropic organs respond with equal facility in either position. 
The action of gravity upon a plant may be neutralized by plac- 
ing it on the periphery of a wheel revolving in a vertical plane, 
or by turning the plant on its own axis in a horizontal position. 

EXPERIMENT 67. 

NEUTRALIZATION OF INFLUENCE OF GRAVITY. 

Take the hands from a large wall-clock whose dial is parallel to 
the rays of sunlight (to avoid the disturbing action of light) and 
fasten to the prolonged axis a cork plate 10 cm. in diameter, or a 
wheel to the periphery of which are attached pieces of cork. 
Fasten seedlings of Pea to the cork in various positions by means 
of pins, and set the clock in motion. Twenty-four hours later each 
seedling will be found to be growing in the position in which it was 
placed, and no marked curvatures in any of the organs can be 
noticed. (Fig. 50.) 

Remark. — The revolving wheel must be partially immersed in water or 
placed in a spray to keep the seedlings moist. A small American clock 
can be used instead of the large clock shown in the figure. 

45. Replacement of Gravity. — -When gravity is overcome by 
another force, the seedling tends to place its axis parallel to this 
new force in the same manner as toward gravity in its normal 
position. The force which acts upon a plant fastened to a 
rapidly-revolving wheel acts in a tangential direction ; conse- 
quently the plant tends to place its axis parallel to the tangent. 
This is true of plants rotated in a vertical plane at a speed of 
100 to 300 revolutions per minute with a wheel having a radius 
of 6 to 20 cm. If a plant is rotated in a horizontal plane at 
this speed, centrifugal force tends to cause the shoot axis to 
lie in a horizontal plane, while gravity tends to cause tlie 
axis to take a vertical position. In this instance the axis will 
take a position between the direction of these two forces. 



56 



EXPERIMENTAL PLANT PHYSIOLOGY, 



The roots will point outward and downward, and the shoots 
upward and inward. These positions will be taken by rapidly- 
growing seedhngs in 5 or 6 hours. 

EXPERIMENT 68. 

REPLACEMENT OF GRAVITY BY CENTRIFUGAL FORCE. 

If a water system is at hand, the rapid rotation of the wheel or disk 
holding seedlings may be accompUshed by the following apparatus 

Fig. 51. 




Centrifugal apparatus. (After Oels.) ^, heavy board base ; By cork hold- 
ing the sealed end of a glass tube which serves as a bearing for the end 
of the axis of the wheel. 

and the seedlings may be kept moist during the experiment. Upon a 
wire, 40 centimeters long, the size of a knitting-needle, are strung at 
equal distances a number of circular cork plates, 3 cm. in diameter 
and a half-centimeter thick. The wire is now bent in the form of a 



IRRITABILITY. 57 

circle, the ends brought together through a piece of cork and united. 
Four brass wires serve as spokes, while the hub is made from a 
heavy cork. The axis is also made from a piece of wire, about 15 
cm. in length, in order that the seedlings may have enough space 
for their curvatures. The axis rests in bearings made of the ends 
of sealed glass tubes (Fig. 51,^), which are fastened in stationary 
corks by means of sealing wax. If now a sufficient stream is al- 
lowed to fall perpendicularly on the cork plates on one side, a 
rapidity of revolution will be secured that will in five or six hours 
effect a noticeable change in position of the seedlings, which have 
been placed with their roots toward the center. If large casks are 
at hand, the experiment may be carried on without a water system. 
A glass tube of an internal diameter of 4 mm. with a fall of i meter 
of the water will furnish a stream that will revolve the wheel more 
than twice per second, which is entirely sufficient for the experi- 
ment. The replacement of the water is necessary for the continua- 
tion of the experiment. 

46. Heliotropism, Thermotropism^ etc. — Radiant energy in 
the form of heat, light, and electricity exercises a very marked 
directive influence on the position of plant-organs. The effect 
of sunlight is much better know^n than that of the other stimuli 
acting on the plant. It is a matter of general observation 
that the shoots of a large number of plants bend toward the 
light. A close inspection shows that various organs respond 
in a different manner to light, as also to gravity. Thus 
many roots direct themselves away from the source of light 
(apheliotropisnt)^ trailing shoots, leaves, etc., at right angles tO' 
the rays {diaheliotropisin)^ while, as noted above, others, such 
as stems, bend toward the light {^proJicliotropisin), It will be 
seen that while the force of gravity acts always in tht- same 
direction, the line of light-rays from the sun moves through 
an angle of 180 degrees daily. This change of the position of 
the source of light causes corresponding movements in helio- 
tropic organs. Sunlight affords two separate stimuli to the 
plant : one from the blue-violet rays which causes helio- 



58 



EXPERIMENTAL PLANT PHYSIOLOGY, 



tropic movements, and one from the red end of the spectrum 
which causes heat or thermotropic movements, as may be 
shown by Experiment 72. The purpose of the heHotropic as 
well as all other movements of plants is doubtless that of plac- 

FiG. 52. 





Diagram of light positions of leaves. The arrows denote the direction of 
the rays. (Vochting.) 

ing the plant-organ in the position best suited to the perform- 
ance of its functions. HeHotropic movements place the leaves 
in a position most favorable for photosynthesis and transpira- 
tion. 



IRRITABILITY. 



59 



EXPERIMENT 69. 

PROHELIOTROPISM. 

Place a Malva or Helianthus grown in a pot in the open air, 
near a window with a southern exposure. The leaves gradually 
assume the definite positions shown in Fig. 52. 

EXPERIMENT 70. 

HELIOTROPIC MOVEMENTS OF ROOTS AND SHOOTS. 

Fasten seedlings of Sinapis alba (Mustard) or Phaseolus multiflo- 
rus (Bean) on a piece of tulle stretched lightly across a glass vessel 

Fig. 53. 





Mm 







Dark chamber with a tube opening in one end. (Schleichert.) 
filled with spring-water. After the roots and stems have attained a 



Fig. 54. 



length of I cm. place the apparatus 
under a pasteboard box lined with 
black paper, through which the 
light may gain entrance by a small 
aperture. In a few hours the roots 
and stems will be influenced as de- 
scribed above. (Figs. 53 and 54.) 

EXPERIMENT 71. 

HELIOTROPIC MOVEMENTS OF LEAVES. 

Bend and fasten in a horizontal 

position an upright well-leaved 

branch of the Ma])]e, or a whole 

^ ^,. ^ ^^ , , Helianthus plant, in the open air. 

beedhng of Mustard grown under 
one-sided illumination. (Det- Soon the leaves which were previ- 

"^^^0 ously horizontal, and perpendicu- 

lar to the shoot on all sides, show peculiar torsions of the petioles, 




6o EXPERIMENTAL PLANT PHYSIOLOGY, 

which, so far as they are capable of growth, finally result in the 
placing of the leaves in a horizontal position, but parallel to the 
shoot and one another. (Fig. 55.) 

EXPERIMENT 72. 

EFFECT OF RED AND BLUE LIGHT. 

Of two equally sensitive seedlings, place one in a chamber (Fig. 
55), with one side of yellow glass, and the other in a similar chamber, 
with one side of blue glass. The heliotropic movement is much more 
marked in the blue light. Instead of the colored plates, use glass 
vessels with parallel walls, filled, one with a solution of bichromate 

Fig. 55. 




Shoot of Sunflower which has been in a horizontal position several days. 

(After Oels.) 

of potassium, the other with a solution of ammonia-copper-oxide. 
Only small plants can be used in the experiment. 

EXPERIMENT 73. 

HELIOTROPIC REACTION OF PLANT WITH GRAVITY NEUTRALIZED. 

If the influence of gravity is removed from a plant as in Experi- 
ment 67, and the light allowed to fall parallel to the axis of the 
plant, the roots and shoots will be seen to take opposite direc- 
tions in a plane parallel to its rays. 

EXPERIMENT 74. 

THERMOTROPISM. 

Grow seedlings of Corn in a pot, and place in a position where 
the light will be received perpendicularly. At a distance of 40 cm. 
place a sheet of smoked tin which is kept warm by a spirit-lamp. 
In twenty-four hours the shoots will have inclined toward the 
source of the heat. Repeat the experiment with Peas. 



IRRITABILITY, 



6i 



47. Periodic Movements. — The sun is continually changing 
its position during the day ; consequently if a leaf remains in a 

Fig. 56. 





Fig. 57. 



Day and night positions of leaflets of Bean. (Detmer.) 
fixed position it receives the maximum heat and light at one 
moment only. It is found that leaves not only exhibit move- 
ments corresponding to the heat and light received, but also 

assumed certain positions 
to avoid excess or loss of 
heat. An organ loses or 
receives the least heat 
when its long axis is 
vertical. A great num- 
ber of these movements 
have been described as 
*' sleep movements." 
EXPERIMENT 75. 

SLEEP MOVEMENTS. 

Observe the positions of 
Sleep position of leaves of Oxalis induced the leaflets of a seedling of 
by artificial darkness. (Hansen.) ^^^^ ^^ ^^ ^^ Oxalis, grow- 

ing in the sunlight, at 8 a.m., i p.m., and 6 p.m. Determine whether 
these positions are due to light or heat by use of the dark chamber. 
(Figs. 56 and 57.) 




62 EXPERIMENTAL PLANT PHYSIOLOGY, 

48. Hydrotropism. — The moisture of the medium which 
surrounds the plant induces movements in certain organs 
either toward or away from the source of the moisture. The 
property of an organ by which it reacts to moisture is termed 
hydrotropism. By this power roots direct their apices toward 
portions of the soil containing the proportion of moisture best 
suited to their specific needs. 

EXPERIMENT 76. 

HYDROTROPISM OF ROOTS. 

Cover a zinc box, 5 cm. wide and 20 cm. long, open on two sides^ 
w^ith gauze after it has been filled with moist sawdust, containing 
swollen seeds of Bean, Pea, or Fig. 58. 

Corn. Suspend the apparatus 
under a pasteboard box, so that it 
hangs at an angle of 45 degrees. 
After a time the roots issue through 
the openings in the gauze beneath ; 
they do not follow geotropism and 
grow directly downward, however, 
but press against the layer of moist 
sawdust. Place the apparatus in a 
damp chamber where the moisture 
is equal in all directions from the 
roots, and they grow directly down- 
ward in response to the stimu- 
lus of gravity. In this case the 
roots receive the same stimulus 
from moisture in all directions, 
and in consequence no reaction to 
it is shown. They are free to re- Hydrotropism of roots. (Detmer.) 
spond to their progeotropic tendency. 

49. Contact Movements. — Many plants will exhibit move- 
ments so rapid as to be visible to the naked eye when touched 
or struck with any hard object. These movements serve vari- 
ous purposes in different groups of plants. In some instances, 
as in the Mimosa, this is a device for protecting the leaves 




IRRITABILITY. 



65 



from injury. By this "' sensitiveness " of tendrils, climbing 
plants are able to attach themselves to supports and lift their 
leaves to sunlight. In certain carnivorous plants, such as Dro- 
sera and Dionaea, the rapid movement of the tentacles and 
leaves -enables these plants to capture insects which are held 
and whose substance is absorbed by the plant. 

EXPERIMENT 77. 

MOVEMENTS OF SENSITIVE-PLANTS. 

Grow Mimosa pudica (Sensitive-plant) from seed, in a pot^ 
Moisture and temperature of about 20° C. are necessary for the welfare 

Fig. 59- 




Mimosa pudica. The leaf on the left is in a normal position ; the one on the 
right has been stimulated. (Detmer.) 

of the plant ; consequently it should be kept under a bell-jar slightly 
raised at one side to allow for ventilation, and placed in the sun- 
shine. Try the following experiments : a. Jar the entire plant by 
striking the pot. In a few seconds the leaves take the position 
shown in Fig. 59. b. Strike one of the terminal leaflets„ The i)airs 
of leaflets fold up together in succession, and finally the whole leaf 
sinks on its petiole, c. Touch the upper side of the pulvinus with 
a pointed object. No movement follows, d. Touch the under side 
in like manner. A movement results, e. With a sharp knife cut off 
the petiole just above the pulvinus. A drop of water issues from the 
lower surface, which in an uninjured leaf would pass into the leaf-stalk. 



64 EXPERIMENTAL PLANT PHYSIOLOGY, 

EXPERIMENT 78. 

MOVEMENTS OF STAMENS. 

Touch Stamen-filaments of Centaurea, Carduus, or Cichorium. 
The filaments contract. 

Fig. 60. 




Tendrils of Bryony. (Kerner.) a, young tendrils ; b b, nearly mature and 
very highly irritable ; c r, two tendrils which have intertwined. 

EXPERIMENT 79. 

CURVATURE OF TENDRILS. 

Touch a tendril of the Passion-flower, Bryony, or Squash on 
the concave surface near the tip with a pencil and observe carefully. 



IRRITABILITY, 



65 



In a time varying from 30 seconds to several minutes a curvature is 
begun. Note rapidity, extent, and duration. Place a small rod in 
contact with the tendril. In a few hours it will have coiled around 
it. Observe the formation of spirals in the free portion of the 
tendril. (Fig. 60.) 

EXPERIMENT 80. 

RELATION OF HARDNESS OF OBJECTS TO CURVATURE PRODUCED IN TENDRILS. 

Test the effect of water, mercury, soft gelatine, glass, iron, and 
wooden objects when brought in contact with tendrils. 

EXPERIMENT 81. 

ACTION OF LEAVES AND TENTACLES OF CARNIVOROUS PLANTS. 

Obtain several plants of Sundew (Drosera) from the swamps. 
In digging them, care should be taken to leave a large mass of the 
soil on the roots of each so that their growth may not be greatly 
disturbed. Cover with a bell-jar and place in the sunlight. Touch 



Fig. 61. 



Fig. 62. 





Leaf of Dionaea expanded. 
(Kerner.) 



Leaf of Drosera with right leaf half 
contracted. (Darwin.) 



the tentacles with small pieces of a large variety of substances, 
wood, sugar, starch, paste, alkali, meat, bits of stone, etc., and note 
to what substances the tentacles react and the rapidity of move- 
ment. Repeat with Dionaea. 



66 EXPERIMENTAL PLANT PHYSIOLOGY. 

50. Circumnutation. — If the tip of a shoot of some rapidly- 
growing plant, such as the Pea or Bean, is kept under observa- 
tion for several minutes, it will be seen that it slowly changes 
position ; and if the time of observation is extended, it will be 
found that it inclines successively toward every point in the 
horizon. In some plants the movement is in the same direc- 
tion as the hands of a watch, and in others it is in the contrary 
direction. This nutatory movement of growing tips is quite 
generally distributed among plants, but it is most marked in 
twining stems. The causes which produce the movement are 
chiefly inequalities in growth extension of the sides of the 
stem, and the reaction to the influence of gravity. 

EXPERIMENT 82. 

CIRCUMNUTATION OF SHOOTS AND TENDRILS. 

Note the positions of a growing tendril of the Gourd, Pea, 
Bryony, or Wild Balsam Apple at intervals for three hours. 

Plant three or four seedlings of the Scarlet Runner or commoi. 
Bean at equal distances from one another in a circle around an 
upright post. Mark the successive positions of the tips of each 
until it becomes twined around the support. 

51. Hygroscopic Movements. — Many plants are provided with 
cells which take up or lose water in such manner as to give 
rise to very marked movements in the organs of which they 
form a part. Such cells are found in the leaf-blades of a large 
number of Grasses, and other plants which inhabit arid regions. 
In such plants this is a provision for rolling up the leaves in 
a form which will prevent undue loss of moisture from the 
organ. By a similar action many anthers open and allow the 
escape of the pollen, and fruit-capsules allow seeds to escape* 
In the latter instance sufficient force is sometimes furnished 
to throw the seeds to a distance or bury them in the soil. 



IRRITABILITY. 



Fig. 63. 



EXPERIMENT 83. 

WARPING OF WOOD. 

Wipe the adhering moisture from a thin piece of wood, such as 
a cigar-box lid, which has lain in water 24 hours, and fasten to 
another piece of similar size which is air-dry, by means of a number 
of small nails. Lay in a dry place. The loss of moisture from the 
saturated piece will cause the double board to become curved. 

Note the " warping " of unseasoned timbers. 

EXPERIMENT 84. 

MOVEMENTS OF FRUIT-CAPSULE OF IMPATIENS. 

Bring some fruit of Balsamina (Impatiens noli tangere) which 
is nearly ripe into warm dry air. (Hold 
at a distance above a gas-flame.) The 
outer covering of the fruit contracts and 
forcibly ejects the fruit. Make sections 
of the portions of the capsule, and describe 
the action of the hygroscopic cells. 

EXPERIMENT 85. 

TWISTING MOVEMENTS OF THE BEAK OF AN 
^ ,. ERODIUM SEED. 

Erodium seed With the long 
beak twisted by drying. A moist seed of Erodium is placed 

(Detmer.) \q\x}[i the point in a damp soil. In drying 

the beak curves and twists in a spiral form. If the twisting of the 
beak is hindered by a piece of wood thrust into the sand beside it, 
the force will be exerted upon the seed, and will be thrust into the 
sand still deeper. (Fig. d^?^ 




CHAPTER VI. 

GROWTH. 

52. Nature of Growth. — The increase of the Hving substance 
of an organism is designated growth, and it is generally accom- 
panied by an increase in weight and size. This increase does 
not, however, always accompany growth; indeed, it was de- 
monstrated in Experiment 29 that a plant may grow while 
losing in weight. If the plant is accumulating storage material 
it will, on the other hand, undergo an increase in weight not in 
any manner connected with growth. It is also to be noted 
that independent changes in form and size occur which are due 
simply to alterations in the force of turgor and in the extensi- 
bility of the cell-walls. Lastly, growth does not consist in the 
formation of new cells ; on the contrary, the formation of new 
cells is a result of growth. 

EXPERIMENT 86. 

MEASUREMENT OF GROWTH EXTENSION. 

To determine the increase in length of a plant the simple auxa- 
nometer shown in Fig. 64 will be found fairly accurate. This appa- 
ratus consists of an upright stand 50 cm. in height to which is 
attached a horizontal arm 10 cm. in length. To the end of this 
arm is attached a wooden pulley 4 cm. in diameter, in such manner 
that it will turn freely. To one side of this pulley is fixed a thin 
wooden pointer 20 cm. in length. This pointer is made from a 
strip not more than 2 mm. in thickness, and has wrapped around 
the larger end at ^ a sufficient quantity of tinfoil to balance the 
longer end. A curved paper-scale ruled to 2 mm. is held by 
another stand near the tip of the pointer. A linen or silk thread 

68 



GROWTH. 



69 



is tied to the tip of a shoot of a Coleus, Tomato, or Potato, or 
leaf of a Narcissus grown in a pot. The plant is set directly 
under the pulley and the string is passed over the pulley, and 
attached to this end is a weight G of one gram or more to keep the 
threat taut. As the plant grows in length it allows the weight 
G to descend, turning the pulley as it does so. The pointer is at- 
tached directly to the pulley, and as the elongation takes place it 

Fig. 64. 




Lever auxanometer. (After Oels.) Z, lever; g, balance-weight on lever; 
G^ counterpoise to keep the string taut ; /, string. 

passes downward along the scale. Since the length of the pointer 
from the center of the pulley is 16 cm. and the radius of the pulley 
is 2 cm., the amount of growth is magnified 8 times. The apparatus 
is set up with the pointer at zero on the upper end of the scale. 
Observations of its position should be made at least three times 
daily. A growth extension of i to 5 cm. daily may be expected 
under favorable circumstances. 



70 



EXPERIMENTAL PLANT PHYSIOLOGY, 



Fig. 65. 



EXPERIMENT 87. 

MEASUREMENT OF ROOT EXTENSION. 

Germinate Pea, Bean, or Squash seeds until the primary roots 
are 2 cm. in length. Place one of the seed- 
lings in the bowl of a thistle-tube or small 
^' funnel, with the root depending downward in 
the tube. Cover the seedling with moist 
cotton and place the bottom of the tube, in 
a vessel of water. By means of India ink 
mark off intervals of 2 mm. on the tube, and 
set the whole apparatus in a light equal in 
all directions. Note the position of the 
root-tip at least twice daily. A growth of 4 
to 20 mm. in a day may be expected. 

Focus a horizontal microscope with a 
power of 25 diameters on the extreme tip of 
the root. It will be seen to move slowly 
across the field of view. (Fig. 65.) 

EXPERIMENT 88. 

MEASUREMENT OF GROWTH INCREASE BY WEIGHT. 

Select a young Squash or Pumpkin which 
has attained a diameter of a few centi- 
meters and place on the pan of a druggists* 
balance (Fig. 24), with the vine supported in 
such a manner that it bears as little weight as 
possible on the balance. Place in the second 
pan sufficient weights to establish an equilib- 
rium. Equalize the scale morning, noon, 
and evening, and the amount of increase may 
be directly obtained. During the period of 
most rapid growth the daily increase will 
amount to 200 to 700 grams. At times the 

Seedling of Squash in a weight of the fruits will be found less at 
thistle-tube. (Detmer.) , . , . . 

noon than m the mornmg owmg to excessive 

evaporation of water from its surface and that of the leaves. 

53. Grand Period of Growth. — With regard to grovi^th three 
regions may be observed in any organ composed of many 
cells : one in which new cells are constantly forming, as in 
the tips of roots and shoots ; another in which the cells are in- 




GRO WTH, 



71 



Fig. 66. 



creasing in size, and a third in which the cells have attained 
their full size and maturity. The time inclusive of the forma- 
tion and enlargement of a cell is termed its grand period of 
growth. In the case of an organ, this period includes the times 
from the formation of all of its cells to their maturity. All of 
the cells are not formed at the same time and do not reach 
maturity at the same time. The portion containing the cells 
Avhich are enlarging most actively is designated the zone of 
maximum growth. This zone is constantly changing its posi- 
tion, as may be seen in the following experiments. 

EXPERIMENT 89. 

ZONE OF MAXIMUM GROWTH OF ROOTS. 

Select a healthy seedling of Pea, Bean, or Squash with a root- 
let 2 cm. in length. With a pointed 
camel's-hair brush mark off ten in- 
tervals I mm. apart. Place the seed- 
hng in a thistle-tube as in Experiment 
87. Set where it may receive an equal- 
sided illumination. In twenty-four 
hours observe the length of the inter- 
vals. The fourth, fifth, sixth, and 
seventh from the tip will be found to 
have elongated much more than any 
of the others. Twenty-four hours 
later the terminal division will have 
partaken of this elongation, showing 
that the zone of maximum growth 
moves steadily toward the tip. Now 
follow the growth of the second inter- 
val. At the beginning of the experi- 
ment it elongates somewhat slowly at 
first, then more rapidly, until it is grow- 
ing more rapidly than any other por- 
tion of the root. Its rate then de- 
creases until it finally ceases. In the e ji- r r. /^ ^ x 
^ Seedlings of Pea. (Sachs.) 




mean time the next interval toward the 
tip begins to increase in rapidity. 



Showing zone of maximum 
growth. 



^2 EXPERIMENTAL PLANT PHYSIOLOGY. 

and about the time the previous one has begun to lessen its rapidity 
of growth, it has reached its maximum. In this manner the zone of 
maximum growth progresses. (Fig. (}(>.) 



EXPERIMENT 90. 

ZONE OF MAXIMUM GROWTH OF STEMS. 

Growth of stems may be observed in the same manner as in the 
last experiment. The elongation of the natural divisions, the inter- 
nodes^ can be measured and compared with one another. The 
elongating part is greater than in roots — 35 millimeters in the Bean. 
The internodes vary in length ; the middle ones are the longest. 
Satisfactory results may be attained by the measurement of centi- 
meter intervals on the stem of Bean or Corn. Compare movement 
of zone of maximum growth with that in roots. 

EXPERIMENT 91. 

ZONE OF MAXIMUM GROWTH OF LEAVES. 

Cultivate Gourd or Tobacco plants in large pots, and after some 
leaves have been formed place them under large bell-jars, and set 
in light, but not in direct sun light, in a temperature as nearly 
constant as possible. Before doing this mark off on the petiole or 
midrib of a young leaf a scale as above. Compare observations 
with results of above experiments. 

54. Influence of Light on Growth. — While light is necessary 
for the formation of food by photosynthesis, and for the per- 
formance of certain other functions, it at the same time 
generally retards growth. Only the blue-violet end of the 
spectrum exercises this retarding influence. By reason of 
this influence the maximum growth of a great number of plants 
occurs after they have been deprived of light for the longest 
period, which is in the morning, or just before daylight. 
Temperature is generally more favorable to growth during the 
afternoon, and as a consequence the plant grows rapidly at 
this time also. In fact the maximum growth often occurs then. 




GROWTH. 73 

Light also influences the form and size of the cells, as well as 
of the entire plant. (See §40.) 

EXPERIMENT 92. 

GROWTH OF SEEDLINGS IN DARKNESS. 

Grow seedlings of Cucurbita (Squash) in similar pots, some of 
which are set in the light, and others y\g. 67. 

are covered by a pasteboard box, at 
the same temperature. The latter do 
not develop normally ; the shoot axes 
are much extended, and form only im- 
perfect leaves, which assume an up- 
right position. (Fig. 67.) All parts 
of the plant are pale and dispropor- 
tionately tender. The lignification of 
the ^vood is hindered, in consequence CucurbitaseeQungs. (Detmer.) 
of which there is no opposition to the a, grown in darkness ; b, 
extension of the tissues by the turgor grown in light, 
stretching of the parenchyma-cells. 

Remark. — Care must be taken in this experiment that both plants do 
not stand in the sunlight, otherwise an abnormally high temperature will 
arise in the pasteboard box, and thus the relations of temperature will be 
altered. 

EXPERIMENT 93. 

COMPARISON OF GROWTH OF SEEDLINGS IN LIGHT AND DARKNESS. 

Germinate a number of Peas in a pan of moist sawdust until the 
main roots are 2 cm. long. After the roots of several, as nearly 
alike as possible, have been marked with a scale, as in Experiment 
89, place some in the light, and others under a pasteboard box, over 
spring-water. It will be found that the growth in light is less than 
in darkness. At the same time the daily period of growth can be 
observed. 

55. Influence of Light upon the Anatomy of the Leaf. — The 

leaves of common trees have in the upper side a closely- 
arranged layer of cells rich in chlorophyll (^palisade parcnclLyind)y 
and in the lower side a loosely-arranged tissue poor in chloro- 
phyll {spongy par encJiy ma). This arrangement depends upon 
the influence of light. Shaded leaves exhibit another struc- 



74 EXPERIMENTAL PLANT PHYSIOLOGY, 

ture, and leaves which have been artificially twisted, so that 
the lower side is exposed to the light, reverse the arrangement 
of these two kinds of parenchyma. 

EXPERIMENT 94. 

INFLUENCE OF LIGHT ON THE STRUCTURE OF LEAVES. 

Turn and fasten young leaves of the Beech (Fagus sylvatica) so 
that the under side is exposed to the light. When mature they 
show palisade tissue in the side now above, and spongy parenchyma 
in the side turned away from the light, as may be seen on examina- 
tion with the microscope. 

EXPERIMENT 95. 

DEVELOPMENT OF FLOWERS IN DARKNESS. 

Enclose a young inflorescence of Scarlet Runner or Morning- 
glory in a pasteboard box or bag of thick black cloth. The flowers 
and fruit will develop normally in the darkness thus secured. 

56. Influence of Gravity and Light on the Formation of Organs. 

— Light and gravity influence the origin and demarkation of 
the forms of organs in a very remarkable manner. If a twig 
of Willow or some other plant is placed in a damp chamber, 
root and leaf buds will develop under the bark. If the twig is 
placed in an upright position, the roots will develop below and 
the leaves above. This " polarity " is, according to Vochting, 
due to light and gravity. The action of light induces the 
formation of shoots on the illuminated side, and roots on the 
shaded portion. That gravity acts in a similar manner may 
be shown under other conditions. If a Willow twig is rapidly 
turned, like the diameter of a wheel (Experiment 68), shoots 
will be formed near the center of revolution, and roots at 
the peripheral ends. The symmetry of flowers, according to 
Vochting's researches, is due to the influence of gravity. 



GRO WTH, 



75 




EXPERIMENT 96. 

COMPARISON OF THE GROWTH OF CUTTINGS IN LIGHT AND DARKNESS. 

Fasten a Willow twig in an upright position in a covered glass 

cylinder containing some water, and set in the sunlight. It develops 

roots below and shoots above. Another twig treated in the same 

Fig 68 manner but placed in the dark acts similarly. (Fig. 

EXPERIMENT 97. 

influence of LIGHT ON THE FORMATION OF ROOTS AND SHOOTS. 

Set up the experiment as above, but place the cylin- 
der in a pasteboard box which 
admits light at the side through 
a long slit. Roots develop on the 
side of the shoot away from the 
light, and shoots on the illumi- 
nated side. 

EXPERIMENT 98. 

DEVELOPMENT OF ROOTS AND SHOOTS 
IN A REVERSED POSITION. 

Suspend a Willow twig in a 
reversed position in a glass cylin- 
der furnished with water, in the 
light. A contest arises between 
the specific tendency of the twig 
to form shoots on the original 
upper end, and roots on the lower 
end, and the influence of light 
69. Willow twig in reversed position. ^^^ gravity which directly op- 
(Hansen.) a, original upper end ; pose it. At first the habit of 

b, original lower end. ..u 1 i. -i j i. 

^ the plant prevails, and roots are 

formed on the upper, shoots on the lower end. Then the influence 

of the physical forces is manifested by the development of roots on 

the lower and shoots on the upper end of the twig. (Fig. 69.) 

57. Influence of Temperature on Growth. — For every plant 
there are five important temperature divisions : ist, destructive 
cold, a low temperature producing death by the disorganiza- 
tion of the protoplasm ; 2d, specific zero, which arrests the 
activity of the protoplasm, but does not necessarily result in 



68. Willow twig in normal position. 
(Hansen.) a, shoots ; b, roots. 



76^ EXPERIMENTAL PLANT PHYSIOLOGY, 

damage to the organism ; 3d, optimum temperature^ in which 
normal development proceeds ; 4th, maximum temperature, 
at which the protoplasmic activity comes to a standstill without 
necessarily injuring the organism ; 5th, destructive heat, pro- 
ducing death by disintegration of the protoplasm. These divi- 
sions vary greatly with each species. 

58. Sources of Heat. — The temperature of any plant is the 
result of the heat it receives from several sources. A portion 
comes directly from the heat-rays of the sunlight, as well 
as from the light-rays which it is able to convert into heat by 
means of chlorophyll, anthocyanin, and other coloring matters. 
Another portion is received from the soil, which is generally 
more constant in temperature than the air. According to 
Kerner the soil of a mountain at a height of 2200 meters is 
3.6° C. higher than the surrounding air. Another and by no 
means unimportant source of heat is the combustion of the 
carbon compounds in the plant. (See Experiment 53.) 

59. Influence of Temperature on Geographical Distribution. — In 
consequence of the obliquity of the ecliptic, no place on the 
earth has the same temperature during the entire year, disre- 
garding even the changes of day and night. Fluctuations in 
temperature vary greatly with the locality : it is greater in 
valleys and at the poles than it is on mountains and at the 
equator. Fluctuation further depends upon the continental or 
oceanic position of a place. Again, between the elevated cold 
regions of the warmer zones and the polar regions there is the 
difference of short period of daylight and the long summer on 
one hand and the longest period of daylight, and a short 
summer on the other. These conditions of temperature, to- 
gether with those of rainfall and soil, are the most important 
factors in the geographical distribution of plants. The regions 
which are not subject to extremes of temperature will be found 



GROWTH, 77 

most suitable for the greater number of species. While some 
species of plants thrive with a low summer heat if the tempera- 
ture does not sink to the destructive point in winter, others 
endure a low temperature in winter very well if the tempera- 
ture ascends high enough in summer to permit normal fruit- 
formation. 

60. Freezing of Plants. — Formerly it was believed that the 
cell-sap was frozen by cold, that by the resultant expansir i 
the cell-walls were torn, and in this way the plant was ki) .ed. 
It has, however, been demonstrated that a mechanical de truc- 
tion of the cell by rupture does not take place, for t/ie ice- 
formation goes on only in the intercellular spaces, or, in the 
simpler plants, in the water thrown out around the plant. It 
is therefore now held that death by cold is the result of a 
chemical process, which can occur at a temperature even above 
freezing-point. 

Rapid or slow thawing of frozen plants has no influence 
upon the life-energy of the plants. If, however, frozen plants 
which are not killed are thawed slowly, the cells can reabsorb 
the water from the melting ice-crystals around them and regain 
their former turgor. If thawed rapidly, a portion of the water 
of the ice-crystals is evaporated or driven away, and the cells 
cannot regain their turgor. When a plant remains frozen for 
some time, the water slowly evaporates from the crystals and 
the plant is eventually dried. Therefore frozen plants may be 
killed by loss of water, either through continued cold or rapid 
thawing. ; 

Salt solutions freeze at lower temperatures than pure water, 
and in their freezing the water is separated out in the form 
of crystals. Cell-sap, a solution of several stable substances in 
water, acts similarly, and plants may therefore endure a tempera- 
ture many degrees below freezing-point without being frozen. 



78 EXPERIMENTAL PLANT PHYSIOLOGY. 



EXPERIMENT 98. 

FREEZING OF A SALT SOLUTION. 

Partially freeze a solution of potassium bichromate or copper 
sulphate. The frozen portions are distinguished from the concen- 
trated fluid by the paler color. The freezing begins at a tempera- 
ture a few degrees below zero C 

EXPERIMENT 99. 

FREEZING OF A BEET. 

Place a section of a Beet, a centimeter thick, well washed and 
dried, in a dish covered with a glass plate to prevent evapora- 
tion, at a temperj^ture of 6 degrees below zero C. When the 
section is frozen, the surface will be covered with a layer of ice^ 
which when examined with the microscope, at a temperature below 
zero, will be found to consist of parallel crystals. A very heavy ice- 
layer is found on the under side of the section, where it has been 
in contact with the dish. The ice is not colored red, proving that 
not cell-sap but pure water drawn from the cell has been frozen. 
No rupture of the cell-wall occurs in the freezing of living cells, as 
would be the case if the enclosed fluid were frozen. 

EXPERIMENT 100. 

FREEZING OF SPIROGYRA. 

Freeze some Spirogyra filaments in a drop of water on a glass 
slide. After thawing no rupture of the cell-walls appears. 

EXPERIMENT loi. 

FREEZING OF POTATOES. 

Place some Potatoes in < temperature of 5 to 10 degrees below 
zero centigrade, over night. hey are frozen hard, and upon thawing 
become very soft, allowing th sap to be forced out by the lightest 
pressure. Their power of germination is lost, and they easily rot. 
Whether the Potatoes are thawe ^^ quickly or slowly is a matter of 
indifference. 

61, Relation of Moisture to Freezing. — Low and high tem- 
peratures are destructive to plants and plant-organs in propor- 
tion to their richness in w^ater. 



GROWTH, 79 

EXPERIMENT 102. 

FREEZING OF PEA, BEAN, AND WHEAT. 

Place some air-dry seeds of the Pea, Bean, or Wheat for several 

hours in a temperature of 5 to 10 degrees below zero centigrade. 

They do not lose the power of germination, as may be shown. The 

same kinds of seeds when saturated with water are killed by this 

temperature, and are unable to germinate. 

Remark. — Trees behave similarly. In winter, when they contain but 
little water, they endure a high degree of cold ; a late spring frost kills 
them, because the trunks and twigs are full of sap. 

EXPERIMENT 103. 

EFFECT OF HIGH TEMPERATURE ON SATURATED SEEDS. 

Place 30 swollen seeds of Peas or Wheat for a quarter of an 
hour in water at a temperature of 60° to 70° C, and then place in 
a germinator. They do not germinate, while 30 other seeds placed 
in the germinator after soakmg develop normally. 

62. Protoplasm which has been killed by low or high tem- 
perature undergoes molecular changes ; it then becomes per- 
meable to acids and coloring matters. (See § 60.) 

EXPERIMENT 104. 

ESCAPE OF CELL-SAP OF BEET KILLED BY LOW TEMPERATURE. 

Frozen and unfrozen pieces of Beet are placed in water ; the 
first colors the water red, the latter does not. The protoplasm of 
the frozen cells allows the colored sap to pass through it. 

EXPERIMENT 195. 

ESCA. OF SAP FROM A BEET KILLED FY HIGH TEMPERATURE. 

Perform .he above experiment, using pieces of Beet, one of which 
has been in water at a temperature of 60° to 70° C. The result is 
the same as in Experiment 104. 

EXPERIMENT 106. 

ESCAPE OF CELL-SAP CONTAINING OXALIC ACID FROM A STEM OF BEGONIA 
KILLED BY HIGH TEMPERATURE. 

Place two pieces of a petiole of Begonia in distilled water after 
one of them has been treated with water at a temperature of 60° to 
70° C. until colorless. Add a solution of calcium chloride to the 
dishes containing the pieces. The water in one dish remains clear, 



"So EXPERIMENTAL PLANT PHYSIOLOGY, 

while that in the other becomes turbid from the formation of oxa- 
late of calcium. The heated portion permits the escape of oxalic 
acid which it contains. 

63. Loss of Heat. — On account of the importance of warmth 
for the chemical processes in the building up of the plant, 
many plants possess peculiar adaptations for preventing undue 
loss of heat. 

EXPERIMENT 107. 

ADAPTATIONS TO PREVENT LOSS OF HEAT. 

Grow seedlings of Helianthus (Sunflower) and Cucurbita 
(Squash). As soon as the cotyledons are raised above the earth, 
it may be observed that they are extended during the daytime, and 
during the coolness of the evening close together above, whereby 
the loss of heat by radiation is decreased. (See Experiment 75.) 

64. Resting Period. — It is known that the winter buds of 
trees and shrubs can be made to open very early in the spring 
if they are placed in a warm room or greenhouse. In this 
way, shoots cut from Syringa vulgaris (Lilac), or the Willow, 
in February, may be given an early development. It might 
be inferred that these plants are compelled to rest by the winter 
cold and need only heat to set in motion their normal develop- 
ment. This is not, however, entirely true. Experiments have 
shown that the winter resting period is necessary for the plant, 
or rather that it has become accustomed to it by thousands 
of years of habit. It is on account of this acquired habit that 
buds brought into a warm room in January do not begin to 
develop before March, and Potato-tubers brought into a warm 
room in the autumn do not begin to germinate until after 
a resting period of greater or less duration. Potato-tubers 
which are placed in a temperature of zero centigrade, for four 
weeks immediately after digging in August, upon being planted 
in garden soil and watered, will begin the development of 
buds. 



GROWTH. 



EXPERIMENT io8. 

ACCELERATED DEVELOPMEMT OF SHOOTS. 

Cut off twigs of Syringa (Lilac), Cornus (Dogwood), Salix 
(Willow), etc., in several winter months ending with February, and 
place them in water in a warm room, or, better, under a bell-jar to 
keep them moist. The development of the buds proceeds accord- 
ing to the laws given above. 

65. Correlation Processes. — Not all the shoots of a plant come 
to full development. Only the strongest and most useful to 
the whole plant develop, while the others either perish or carry 
on a kind of '' sleep-life." These last are generally styled 
latent buds. If the plant is robbed of a ** concurrent " organ 
by any accident, the nourishment heretofore used by that organ 
is sent to a latent bud, which then emerges from its period of 
rest and develops. Such phenomena are termed correlation 
processes. In gardening much use is made of this capacity of 
the plant ; as, for example, in the formation of thick hedges, 
in the development of branches and flowers y\g. 70. 

on the Fuchsia, etc. 

EXPERIMENT 109. 

DEVELOPMENT OF LATERAL SHOOTS OF THE BEAN. 

Germinate two plants of Bean in pots. Cut 
the epicotyl from one as soon as it appears 
above the ground. Then the buds in the axils 
of the cotyledons develop instead. The otherj 
plant serves as a means of comparison. 

EXPERIMENT no. 

DEVELOPMENT OF LATERAL BUDS OF THE POTATO. 

Place a Potato-tuber with the stem-scar 
underneath in a warm room without the addi- 
tion of water. The buds near the top develop. 
Cut these off and the lower ones start into 
active growth. (Fig. 70.) 

66. External Mechanical Force Exerted by Growing Organs. — 
The growing cells of plants are able to exert a pressure on 




Sprouting Potato. 
(Detmer.) 



82 



EXPERIMENTAL PLANT PHYSIOLOGY, 



bodies surrounding them which may amount to from 12 to 15 
atmospheres. By this force roots and other fixing and ab-^ 
sorbent organs are driven through the soil, and aerial organs 
push their way upward through the air. The total amount of 
energy used in the performance of external work during the 
lifetime of the plant is very great. The spore-bearing cap of a 
Mushroom has been known to lift a weight of 160 kilograms. 
A root of Larch 30 cm. in diameter has lifted a stone 160O' 
kilograms in weight, while a root of a germinating Bean has 
exerted a lateral pressure on the soil amounting to 1.5-4 kilo- 
grams. All growing organs expand with similar force, but in 
the examples given the form of the organ is such as to utilize 
the force in penetrating the substratum. The growing fruit 
of a Cucurbita is capable of exerting a pressure of several 
Fig. 71. thousand kilograms, though it ordi- 

narily meets with no resistance. 
EXPERIMENT iii. 

POWER OF PENETRATION OF RHIZOIDS OF A 
HEPATIC. 

If a Hepatic is placed on several folds 
of moist filter-paper in a chamber satu- 
rated with moisture, within forty-eight 
hours the rhizoids will have pierced the 
filter-paper. The holes through which the 
rhizoids have penetrated were certainly 
not there before. The fibrous structure 
of the paper is so dense that a starch- 
grain of corn, which is only two micro- 
millimeters in diameter, cannot find its way 
through, yet the rhizoids, which are 10 to 
Force exerted by growing 35 micromillimeters in diameter, easily 
roots. (Mangin.) accomplish it. 

EXPERIMENT 112. 

FORCE EXERTED BY GROWING ROOTS. 

To a small upright stand attach a horizontal arm bearing a small 
wooden pulley. Fasten a scale-pan to a cord passing over the 




GROWTH, 83 

pulley to the other end of which is attached a second pan contain- 
ing a 5 -gram weight. Fill the first pan firmly with moist sand, and 
fasten a seedling of Bean in such position that it touches the sand. 
It will push downward into the sand and elevate the weight-pan. 
The scale-pan touched by the root may be suspended directly from 
the horizontal arm by a delicate spiral spring, omitting the pulley 
and second scale-pan. As the root grows it will push the pan 
downward as before, and the distance through which the scale- 
pan moves will indicate the force directly. The strength of the 
spring can . be determined by placing weights on the scale-pan. 
(Fig. 71.) 



APPENDIX. 

ENGLISH AND METRIC WEIGHTS AND MEASURES. 

LENGTH. 

1 micro-millimeter = y^or millimeter or j ^^qq inch. 

I millimeter (mm.) = -^j inch. 

I centimeter (cm.) =: lo mm. = f inch. 

I decimeter (dm.) = loo mm. = 4 inches. 

I meter = 1000 mm. = 39^ inches. 

I inch = 25 mm. 

I foot — 305 mm. or 30^ cm. 

I yard = .91 meter. 

WEIGHT. 

I gram — 15-I grains. 

I kilogram = 1000 grams = 32 oz. Troy or 35^ oz. Avoirdupois. 

I oz. Troy = 31 grams. 

I oz. Avoirdupois = 28 grams. 

I lb. Avoirdupois — 450 grams. 

CAPACITY AND WEIGHT. 

I gram = i cubic centimeter (cc.) = 15^ grains. 
I liter =: 1000 grams, or 1000 cc, or i kilogram = 35^ oz. Avoirdu- 
pois or 32 oz. Troy. 
I pint = 20 oz. Avoirdupois — 567^ grams or 567^ cc. 

CAPACITY (volume). 

I liter = 1000 cc. = i cubic dm. -— if pints. 

I pint = 36 cubic inches = 567^ cc. 

I gallon = 8 pints = 4^ liters. 

I cubic foot = 6 gallons = 28^ liters. 

84 



APPENDIX. 



85 



CENTIGRADE AND FAHRENHEIT THERMOMETER SCALES. 

- 30° Cent. = 

- 25° Cent. = 

- 20° Cent. = 

- 15° Cent. = 

- 10° Cent. = 
" 5° Cent. = 

0° Cent. = 

5° Cent. = 
10° Cent. = 
15° Cent. — 
20° Cent. == 

25° Cent, rrz 

30° Cent. = 
35° Cent. - 



22° Fahr. 


40° Cent. 


r= 


104° Fahr. 


13° Fahr. 


45° Cent. 


— 


113° Fahr. 


4° Fahr. 


50° Cent. 


= 


122° Fahr. 


5' Fahr. 


55° Cent. 


— 


131° Fahr. 


14° Fahr. 


60° Cent. 


— 


140° Fahr. 


23° Fahr. 


65° Cent. 


=r 


149° Fahr. 


32° Fahr. 


70° Cent. 


— 


158° Fahr. 


41° Fahr. 


75° Cent. 


= 


167° Fahr. 


50° Fahr. 


80° Cent. 


— 


176° Fahr. 


59° Fahr. 


85° Cent. 


= 


185° Fahr. 


68° Fahr. 


90° Cent. 


= 


194° Fahr. 


77° Fahr. 


95° Cent. 


=: 


203° Fahr. 


86° Fahr. 


100° Cent. 


= 


212° Fahr. 


95° Fahr. 


110° Cent. 


=:= 


230° Fahr. 



yk' 



INDEX TO PLANT NAMES. 



PAGE [ 

AigCB 6 

Anthemis 45 

Apple 26 

Aroids 45 

Asclepias 32 

Bacteria 3. II> 12, 44 

Balsamina 67 

Barley 48 

Bean, 5, 10, 27, 41, 52, 53. 59» ^o. 

62, 66, 70, 72, 81, 83 

Beech 14. 74 

Beechdrops 11 

Beet 78,79 

Begonia 25, 49, 79 

Bellis 45 

Birch 31 

Bryony • 64, 66 

Buckwheat 5 

Cabbage 14 

Carduus 64 

Carrot » 14 

Centaurea 64 

Cichorium 64 

Coleus 14, 32, 69 

Composite 45 

Corallorhiza 11 

Coral-root 11 

Corn, 5, 8, 10, 20, 27, 34, 37, 52, 

60, 62, 72 

Cornus 81 

Cucurbita 73, 80, 82 

Cuscuta 10, II 

Dahlia 20 

Dionaea 63, 65 



PAGE 

Dodder 10 

Dogwood 81 

Drosera 63, 65 

Elder 18, 33 

Elodea 3^,37,38, 40 

Epiphegus n 

Erodium 67 

Euphorbia 32 

Eagtis 74 

Fritillaria 52 

Fuchsia 81 

Funaria 42 

Fungus II 

Geranititn 14, 20, 42 

Gourd 66, 72 

Grape 18, 19, 20, 36 

Grass 53, 66 

Helia7ithiis 32, 59, 60, 80 

Hemp 44 

Hepatic 82 

Hyacinth 52 

I??ipatie?is II, 14, 34, 67 

Indian-pipe 11 

Iris ^ 14, 24 

Larch 82 

Leontodon 45 

Lilac 80, Si 

Liverwort 14 

Lonicera 29, 31, 32 

Madia 45 

Malva 59 

Maple 59 

Marchantia 25 

Milkweed 32 

87 



88 



INDEX TO PLANT NAMES, 



PAGE 

Mimosa 50, 62, 63 

Mistletoe 10, 11 

Monotropa 11 

Morning-glory 74 

Mosses 14 

Mould II 

Mushroom 11, 82 

Mustard .8, 59 

Myosotis 49 

Na7'cissus 52, 69 

Nettle 19 

Oak 14 

Onion 52 

Oxalis c 60 

Passion-Jlower 65 

Pea, 5, 8, 9, 10, 16, 17, 27, 45, 46, 52, 
53. 55, 62, 66, 69, 70, 79 

Peony » 49 

Phaseolus 53, 59 

Poplar 18 

Potato 26, 69, 80, 81 

Pumpkin o 70 

Raspberry 22 

Rhubarb 18 

Rose 49 

Rosebush 21, 23 

Rust II 



PAGE 

Salix 81 

Sambucus 18, 31, 34 

Scarlet runner .74 

Seaweed 39 

Sensitive plant 50, 63 

Sinapis 59 

Smut , . . . . II 

Sonchus c 32 

Spirogyra 42, 78 

Spurge 32 

Squash. 9, 64, 70, 73, 80 

Sundew o 65 

Sunflower, 18, 19, 20, 29, 32, 60, 76, 80 

Symphytum 23 

Syringa 80, 81 

Toadstool II 

Tobacco o 72 

Tomato 14, 17, 41, 69 

Touch-me-not 34 

Tropaeolum 41, 49 

Tulip 52 

Vaucheria » 42 

Wheat 5, 27, 46, 75 

Wild balsam-apple 66 

Wild lettuce 32 

Willow 18, 34, 74, 75, 80, 81 

Yeast 44 



yd !i - 3^ 



